Peronosporaceae Species Causing Downy Mildew Diseases of Poaceae , Including Nomenclature Revisions and Diagnostic Resources

Abstract

Downy mildew pathogens of graminicolous hosts (Poaceae) are members of eight morphologically and phylogenetically distinct genera in the Peronosporaceae (Oomycota, Peronosporales). Graminicolous downy mildews (GDMs) cause severe losses in crops such as maize, millets, sorghum, and sugarcane in many parts of the world, especially in tropical climates. In countries where the most destructive GDMs are not endemic, these organisms are often designated as high-risk foreign pathogens and subject to oversight and quarantine by regulatory officials. Thus, there is a need to reliably and accurately identify the causal organisms. This paper provides an overview of the Peronosporaceae species causing graminicolous downy mildew diseases, with a description of their impact on agriculture and the environment, along with brief summaries of the nomenclatural and taxonomic issues surrounding these taxa. Key diagnostic characters are summarized, including DNA sequence data for types and/or voucher specimens, morphological features, and new illustrations. New sequence data for cox2 and 28S rDNA markers are provided from the type specimens of three species, Peronosclerospora philippinensis, Sclerospora iseilematis, and Sclerospora northii. Thirty-nine species of graminicolous downy mildews are accepted, and seven previously invalidly published taxa are validated. Fifty-five specimens are formally designated as types, including lectotypification of 10 species, neotypification of three species, and holotype designation for Sclerophthora cryophila.
Citation: Crouch JA, Davis WJ, Shishkoff N, Castroagudín VL, Martin F, Michelmore R, Thines M (2022). Peronosporaceae species causing downy mildew diseases of Poaceae, including nomenclature revisions and diagnostic resources. Fungal Systematics and Evolution 9: 43–86. doi: 10.3114/fuse.2022.09.05

Full text

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© 2022 Westerdijk Fungal Biodiversity Instute 43
Editor-in-Chief
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E-mail:p.crous@westerdijkinstitute.nl
Fungal Systemacs and Evoluon
doi.org/10.3114/fuse.2022.09.05
VOLUME 9
JUNE 2022
PAGES 43–86
INTRODUCTION
Graminicolous downy mildews (GDMs) are diseases caused by
members of the Peronosporaceae (Oomycota, Peronosporales).
GDM pathogens are obligate, biotrophic parasites of culvated
and wild cereals and other grasses in the Poaceae family
(Kenneth 1981, Spencer & Dick 2002). In regions of the world
where the most destrucve GDM pathogens reside, these
diseases can result in signicant crop losses (60–100 %) of
staple food and forage crops such as maize (Zea mays), pearl
millet (Pennisetum glaucum), sorghum (Sorghum spp.), and
sugarcane (Saccharum spp.) (Exconde & Raymundo 1974,
Safeeulla 1976, Kenneth 1981, Rathore et al. 2002, Putnam
2007, Kumar et al. 2012, Li et al. 2020). In parts of the world
where these organisms are not present, foreign GDM pathogens
are oen regulated as quaranne pests by governmental
agencies and are subject to strict control measures to prevent
their spread. For example, in the USA, the maize pathogens
Peronosclerospora philippinensis and Sclerophthora rayssiae
var. zeae pose such a signicant potenal threat to the
country’s agriculture that they are regulated as Select Agents.
Designaon of a plant pathogen as a Select Agent in the USA is
a notable disncon, as there are only seven plant pathogenic
organisms so named, and placement in this category subjects
them to the same general oversight program that also deals
with deadly human pathogens such as the plague bacterium
Yersinia pess, the smallpox virus, and the SARS-associated
coronavirus (SARS-CoV).
Peronosporaceae species causing downy mildew diseases of Poaceae, including nomenclature
revisions and diagnosc resources
J.A. Crouch1*, W.J. Davis1,2, N. Shishko3, V.L. Castroagudín1,2, F. Marn4, R. Michelmore5, M. Thines6
1United States Department of Agriculture, Agricultural Research Service (USDA-ARS), Mycology and Nematology Genec Diversity and Biology
Laboratory, Beltsville, MD, USA
2Oak Ridge Instute for Science and Educaon, ARS Research Parcipaon Program, Oak Ridge Tennessee, USA
3USDA-ARS, Foreign Disease Weed Science Research Unit, Frederick, MD, USA
4USDA-ARS, Crop Improvement and Protecon Research, Salinas, CA, USA
5The Genome Center and Department of Plant Sciences, University of California Davis, Davis, CA, USA
6Goethe University, Department of Biological Sciences, Instute of Ecology, Evoluon and Diversity, Senckenberg Biodiversity and Climate Research
Centre, Frankfurt am Main, Germany
Current address, W.J. Davis: Department of Biological Sciences, Kent State University, Kent, Ohio, USA.
*Corresponding author: joanne.crouch@usda.gov
Abstract: Downy mildew pathogens of graminicolous hosts (Poaceae) are members of eight morphologically and
phylogenecally disnct genera in the Peronosporaceae (Oomycota, Peronosporales). Graminicolous downy mildews
(GDMs) cause severe losses in crops such as maize, millets, sorghum, and sugarcane in many parts of the world, especially
in tropical climates. In countries where the most destrucve GDMs are not endemic, these organisms are oen designated
as high-risk foreign pathogens and subject to oversight and quaranne by regulatory ocials. Thus, there is a need to
reliably and accurately idenfy the causal organisms. This paper provides an overview of the Peronosporaceae species
causing graminicolous downy mildew diseases, with a descripon of their impact on agriculture and the environment,
along with brief summaries of the nomenclatural and taxonomic issues surrounding these taxa. Key diagnosc characters
are summarized, including DNA sequence data for types and/or voucher specimens, morphological features, and new
illustraons. New sequence data for cox2 and 28S rDNA markers are provided from the type specimens of three species,
Peronosclerospora philippinensis, Sclerospora iseilemas, and Sclerospora northii. Thirty-nine species of graminicolous
downy mildews are accepted, and seven previously invalidly published taxa are validated. Fiy-ve specimens are
formally designated as types, including lectotypicaon of 10 species, neotypicaon of three species, and holotype
designaon for Sclerophthora cryophila.
Key words:
biodiversity
downy mildew
new taxa
Oomycota
Peronosporales
plant pathogens
Poaceae
select agents
Citaon: Crouch JA, Davis WJ, Shishko N, Castroagudín VL, Marn F, Michelmore R, Thines M (2022). Peronosporaceae species causing downy
mildew diseases of Poaceae, including nomenclature revisions and diagnosc resources. Fungal Systemacs and Evoluon 9: 43–86. doi: 10.3114/
fuse.2022.09.05
Received: 1 October 2021; Accepted: 20 February 2022; Effectively published online: 8 April 2022
Corresponding editor: P.W. Crous

© 2022 Westerdijk Fungal Biodiversity Instute
Crouch et al.
Editor-in-Chief
Prof. dr P.W. Crous,Westerdijk Fungal BiodiversityInstitute, P.O. Box 85167, 3508 AD Utrecht, The Netherlands.
E-mail:p.crous@westerdijkinstitute.nl
44
As with all organisms capable of incing plant diseases,
reliable and accurate idencaon of the GDM pathogens is
crucial, but idencaon is only possible when the characters
that can be used to idenfy them are clearly known. Any
taxonomic or nomenclatural confusion that would lead to the
misidencaon of species or misapplicaon of a name could
hinder eorts to idenfy introduced species, detect emerging
pathogen threats, and track the spread of disease (Thines & Choi
2016, Petrželová et al. 2017, Davis & Crouch 2022a). However,
this group has never been monographed, and praccal diagnosis
of GDM pathogens is hindered by the absence of an updated,
centralized treatment of the group. Key idencaon resources
such as morphological descripons, diagnosc traits, host
associaons, and molecular datasets for exemplary materials
are currently spread across hundreds of papers spanning more
than 100 years, somemes in obscure and dicult to obtain
publicaons. To our knowledge, one species – Sclerospora
farlowii – has never been illustrated and several species are not
formally typied. The most recent comprehensive taxonomic
reviews of the Peronosporaceae pathogens of grasses were
published more than four decades ago, harkening back to
Kenneth’s summary of the group in 1981 and Waterhouse’s
seminal review in 1964. Since Waterhouse’s review, nineteen
new species, one variety, and ve new genera of GDM pathogens
have been discovered, and molecular phylogenec data has
been used to study these organisms since 2002 (Riethmüller et
al. 2002). Thus, the goal of this paper is to provide an annotated
summary of the names applied to the Peronosporaceae species
causing downy mildew diseases on Poaceae. We briey discuss
the impact of each species, and when possible, summarize
resources and descripons, provide new illustraons, address
nomenclatural issues, and discuss possible research that could
help clarify outstanding taxonomic issues.
MATERIALS AND METHODS
In compiling this treatment, Waterhouse (1964) and Shaw
(1975, 1978) were used as starng points. A literature search
was conducted online using Google Scholar, Index Fungorum,
and MycoBank for publicaons dealing the nomenclature,
taxonomy, and economic impacts of GDM pathogens. Herein,
names of Peronosporaceae species causing downy mildew
diseases of Poaceae are listed alphabecally by the genus they
are currently assigned to. Given the similarity between host and
pathogen epithets throughout this paper, all Lan binomials
are given without abbreviaon throughout the text to avoid
confusion.
Host associaon
The USA Naonal Fungus Collecons (BPI) fungus/host
databases were inially consulted for distribuon and host
informaon (Farr & Rossman 2021). BPI online databases are
cited as Farr & Rossman (2021) to summarize reports of species
listed in “checklist” type publicaons; relevant publicaons
where idencaons were reviewed and veried are directly
cited. The Plant List (hp://www.theplantlist.org), World Flora
Online (hp://www.worldoraonline.org/), and the Germplasm
Resources Informaon Network (GRIN, hp://www.ars-grin.
gov/) were used as sources for plant name synonymy, in that
order. When there were disagreements among the three sources,
preference was given to GRIN. Plant hosts from the original
collecon are listed as current name (synonym, subfamily, tribe)
following Sorgen et al. (2015).
Typicaon and validaon of names
Lectotypes or neotypes were designated for eecvely
published species when original materials and/or specimens
consistent with the protolog were available, following the
current Internaonal Code of Nomenclature for algae, fungi,
and plants (ICNafp; Turland et al. 2018); these are summarized
in Table 1. Names that were not validly described according
to the rules of the ICNafp but represenng disnct taxa are
validated following the ICNafp (Turland et al. 2018). New taxa
and typicaons were registered with MycoBank and are cited
as MB and MBT accession numbers, respecvely. Fungarium
abbreviaons follow the New York Botanical Garden’s Index
Herbariorum (Verkeley et al. 2014).
Idencaon resources
Morphological features for asexual and sexual structures are
summarized in Supplementary Table S1. Diagnoses are provided
for some – but not all – species where sucient traits were
available to provide a reliable diagnosis, but it is important to
note that morphological characteriscs of Peronosporaceae are
inuenced by environment and host (Runge et al. 2012) and may
therefore vary. Full descripons from the species protologs and/
or non-original sources are provided, with protolog descripons
taking precedence and other sources used when the protolog
informaon was incomplete or determined by later authors as
incorrect.
For Peronosporaceae fungarium specimens examined at
BPI and the Canadian Naonal Mycological Fungarium (DAOM)
for this work, macroscopic images of the type specimens were
obtained and are included in this paper as Supplementary Figs
S1–S23.
Line drawings of microscopic features were prepared from
published reference materials and new images of Sclerospora
farlowii (Figs 1–11). Objects and scale bars from original sources
were opened in Photoshop CS6, the contour of objects traced,
then the illustraons were standardized to a uniform style,
with a gray moling represenng cytoplasm and solid grays
represenng solid walls. Thick black lines represent signicant
boundries, such as the ones between cytoplasm and wall. Thin
lines were used to represent delimitaons of vesicles or
zoospores, and dashed lines were used to delineate vacuoles.
As much as possible, drawings were placed at the same scale
to facilitate comparisons of the structures. New microscopic
images were prepared from the type specimen of Sclerospora
farlowii, as illustraons of this pathogen have never been
published. Specimen material was rehydrated in 85 % lacc
acid, stained with coon blue, and visualized using a Zeiss Axio
Imager M2 microscope (Carl Zeiss Microscopy, Thornwood, NY).
Images were captured with an Axiocam 503 color digital camera
using dierenal contrast illuminaon and processed with Zen 2
Pro v. 3.4 soware (Carl Zeiss Microscopy).
DNA sequence data resources are summarized for types
and/or voucher specimens when available. Accession numbers
for nucleode sequences of the barcode markers cox2 and 28S
rDNA were obtained from the Naonal Center for Biotechnology
Informaon (NCBI) GenBank (hps://www.ncbi.nlm.nih.gov/)

© 2022 Westerdijk Fungal Biodiversity Instute
Graminicolous downy mildew pathogens
Editor-in-Chief
Prof. dr P.W. Crous,Westerdijk Fungal BiodiversityInstitute, P.O. Box 85167, 3508 AD Utrecht, The Netherlands.
E-mail:p.crous@westerdijkinstitute.nl
45
Table 1. Summary of type and exemplar materials for Peronosporaceae pathogens of Poaceae. Of the 66 total type specimens, 48 types are newly designated in the current paper (highlighted in bold
text). Basionyms are given if dierent from the current name.
Current name Basionym Specimen Specimen status Year Collected Host Locale Cox2 sequence 28S rDNA
sequence
References
Baobabopsis donbarrei
R.G. Shivas et al.
BRIP 54675 Holotype 2011 Peros rara Australia, Western
Australia
KT248948 KT248945 Thines et al.
(2015)
Baobabopsis enneapogonis
Thines et al.
BRIP 49822 Holotype 2007 Enneapogon
cylindricus
Australia, Northern
Territory
KT248946 — Thines et al.
(2015)
Baobabopsis marneyi R.G.
Shivas et al.
BRIP 70341 Holotype 2019 Enneapogon
polyphyllus
Australia,
Queensland,
Georgetown
OK336436 — Ryley et al. (2022)
Eraphthora butleri (W.
Weston) Telle & Thines
Sclerospora butleri
W. Weston
BPI 187075 Lectotype 1927 Eragross aspera Malawi (formerly
Nyasaland), Bulaki
— — Weston (1933),
this paper
FH 965376 Isotype 1927 Eragross aspera Malawi (formerly
Nyasaland), Bulaki
— — Weston (1933),
this paper
BPI 187074 Might be
isotype?
1927 Collecon
metadata
incomplete
Collecon metadata
incomplete
— — Weston (1933),
this paper
Eraphthora drenthii M. J.
Ryley et al.
DAR 4201 Holotype 1950 Eragross
cilianensis
Australia, New South
Wales
HQ413338 — Ryley et al. (2022)
Eraphthora occultata Y.P. Tan
et al.
DAR 16237 Holotype 1967 Eragross
cilianensis
Australia, New South
Wales
OK391240 — Ryley et al. (2022)
Graminivora graminicola
(Naumov) Thines & Göker
Bremia graminicola
Naumov
LEP4385 Lectotype 1912 Arthraxon
hispidus
Russia, South
Ussuriysk region,
Siberia
— — Naumov (1913),
this paper
BPI 786232 Isotype 1912 Arthraxon
hispidus
Russia, South
Ussuriysk region,
Siberia
— — Naumov (1913),
this paper
LEP4384 Isotype 1912 Arthraxon
hispidus
Russia, South
Ussuriysk region,
Siberia
— — Naumov (1913),
this paper
LEP4377 Isotype 1912 Arthraxon
hispidus
Russia, South
Ussuriysk region,
Siberia
— — Naumov (1913),
this paper
FH
01012075
Isotype 1912 Arthraxon
hispidus
Russia, South
Ussuriysk region,
Siberia
— — Naumov (1913),
this paper
E00297399 Isotype 1912 Arthraxon
hispidus
Russia, South
Ussuriysk region,
Siberia
— — Naumov (1913),
this paper

© 2022 Westerdijk Fungal Biodiversity Instute
Crouch et al.
Editor-in-Chief
Prof. dr P.W. Crous,Westerdijk Fungal BiodiversityInstitute, P.O. Box 85167, 3508 AD Utrecht, The Netherlands.
E-mail:p.crous@westerdijkinstitute.nl
46
Table 1. (Connued).
Current name Basionym Specimen Specimen status Year Collected Host Locale Cox2 sequence 28S rDNA
sequence
References
HUH 738 Voucher 2001 Arthraxon
hispidus
China, Yunnan, A Zi
Ying
KP965747 KP965742 Thines & Göker
(2006)
Peronosclerospora arisdae
J. Kruse et al.
BRIP 67069 Holotype 2018 Arisda
hygrometrica
Australia, Queensland OK336438 — Ryley et al. (2022)
Peronosclerospora
boughtoniae M.J. Ryley et al.
BRIP 14388 Holotype 1978 Sorghum
plumosum
Australia,
Queensland, Lizard
Island
OK33649 — Ryley et al. (2022)
Peronosclerospora
dichanthiicola (Thirum. &
Naras.) C.G. Shaw
Sclerospora
dichanthiicola
Thirum. & Naras.
Illustraon Lectotype 1952 Dichanthium
annulatum
India, Bihar — — Thirumalachar
& Narasimhan
(1952), this paper
Peronosclerospora
eriochloae Ryley & Langdon
BRIP 13693 Holotype 1979 Eriochloa
pseudoacrotricha
Australia, Upper
Pilton, Queensland
— — Ryley & Langdon
(200)1
BRIP 13691 Isotype 1979 Eriochloa
pseudoacrotricha
Australia, Upper
Pilton, Queensland
— — Ryley & Langdon
(2001)
BRIP 13692 Isotype 1979 Eriochloa
pseudoacrotricha
Australia, Upper
Pilton, Queensland
— — Ryley & Langdon
(2001)
FR-0046005 Isotype 1979 Eriochloa
pseudoacrotricha
Australia, Upper
Pilton, Queensland
HQ261813 HQ261786 Telle et al. (2011)
Peronosclerospora
heteropogonis Siradhana
et al.
HOH 898 Holotype 2005 Zea mays India: Rajasthan,
Udaipur
EU116054 — Thines et al.
(2008), this paper
Peronosclerospora ischaemi
M.J. Ryley et al.
BRIP 70369 Holotype 2019 Ischaemum
fragile
Australia, Queensland OK336443 OK350686 Ryley et al. (2022)
Peronosclerospora jamesiae
R.G. Shivas et al.
BRIP 65234 Holotype 2016 Sorghum intrans Australia, Northern
Territory, Wagait
Beach
OK336444 — Ryley et al. (2022)
Peronosclerospora
mactaggari R.G. Shivas et
al.
BRIP 57677 Holotype 2012 Sorghum
morense
Austrlia, Northern
Territory, Dorat Rd.,
Robins Falls
OK336446 OK350687 Ryley et al. (2022)
Peronosclerospora maydis
(Racib.) C.G. Shaw
Peronospora maydis
Racib.
KRAM
O-5859(J)
Lectotype 1897? Zea mays Indonesia, Java, Jawa
Tengah
MW025835 — Suharjo et al.
(2020)
BPI 789413 Isotype 1897? Zea mays Indonesia, Java, Jawa
Tengah
This paper
Peronosclerospora miscanthi
(T. Miyake) C.G. Shaw
Sclerospora
miscanthi T. Miyake
BPI 187301 Neotype 1915 Miscanthus
sinensis
Taiwan: Taipei — — Miyake (1912),
this paper
Stevens
8111
Voucher 1930 Miscanthus
japonicus
Philippines, Luzon HQ261811 HQ261784 Telle et al. (2011)

© 2022 Westerdijk Fungal Biodiversity Instute
Graminicolous downy mildew pathogens
Editor-in-Chief
Prof. dr P.W. Crous,Westerdijk Fungal BiodiversityInstitute, P.O. Box 85167, 3508 AD Utrecht, The Netherlands.
E-mail:p.crous@westerdijkinstitute.nl
47
Table 1. (Connued).
Current name Basionym Specimen Specimen status Year Collected Host Locale Cox2 sequence 28S rDNA
sequence
References
Peronosclerospora noblei (W.
Weston) C.G. Shaw
Sclerospora noblei
W. Weston
DAR 1075 Lectotype 1928 Sorghum
leiocladum
Australia, New South
Wales
— — Weston (1929),
this paper
DAR 1076 Isotype 1928 Sorghum
leiocladum
Australia, New South
Wales
— — Weston (1929),
this paper
BPI 187306 Isotype 1928 Sorghum
leiocladum
Australia, New South
Wales
OK185343 OK255496 Weston (1929),
this paper
FH 965379 Isotype 1928 Sorghum
leiocladum
Australia, New South
Wales
— — Weston (1929),
this paper
Peronosclerospora panici
R.G. Shivas et al.
DAR 35733 Holotype 1980 Panicum
laevinode
Australia, New South
Wales, Narromine
HQ261814 HQ261787 Telle et al. (2011),
Ryley et al. (2022)
Peronosclerospora
philippinensis (W. Weston)
C.G. Shaw
Sclerospora
philippinensis W.
Weston
BPI 187314 Lectotype 1919 Zea mays Philippines, Los Banos — — Weston (1920),
this paper
BPI 187044 Isotype 1919 Zea mays Philippines, Los Banos OK185341 OK181682 Weston (1920),
this paper
BPI 187311 Isotype 1919 Zea mays Philippines, Los Banos — — Weston (1920),
this paper
BPI 187313 Isotype 1919 Zea mays Philippines, Los Banos — — Weston (1920),
this paper
FH 965382 Isotype 1919 Zea mays Philippines, Los Banos — — Weston (1920),
this paper
FH 965383 Isotype 1919 Zea mays Philippines, Los Banos — — Weston (1920),
this paper
Peronosclerospora sacchari
(T. Miyake) Shirai & Hara
Sclerospora sacchari
T. Miyake
BPI 187331 Lectotype 1910 Saccharum
ocinarium
Taiwan — — Miyake (1927),
this paper
BRIP
44241A
Voucher 2004 Saccharum sp. East Timor EU116052 HQ261764 Telle et al. (2011)
Peronosclerospora sargae
R.G. Shivas et al.
BRIP 27691 Holotype 2000 Sorghum
morense
Australia, Northern
Territory
HQ261809 HQ261782 Shivas et al.
(2012)
Peronosclerospora
schizachyrii R.G. Shivas et al.
BRIP 67070 Holotype 2018 Schizachyrium
fragile
Australia, Queensland OK336452 OK350689 Ryley et al. (2022)
Peronosclerospora sehimas
M.J. Ryley et al.
BRIP 49806 Holotype 2006 Sehima
nervosum
Australia, Northern
Territory, Arnhem
Highway, Jabira
OK336453 — Ryley et al. (2022)
Peronosclerospora sorghi (W.
Weston & Uppal) C.G. Shaw
Sclerospora sorghi
(Kulk.) W. Weston &
Uppal
BPI 187336 Lectotype 1915 Sorghum vulgare India, Coimbatore — — Weston & Uppal
(1932), this paper
HUH 897 Voucher 2005 Sorghum bicolor India, Karnataka,
Dharwad
EU116055 — Thines et al.
(2008)

© 2022 Westerdijk Fungal Biodiversity Instute
Crouch et al.
Editor-in-Chief
Prof. dr P.W. Crous,Westerdijk Fungal BiodiversityInstitute, P.O. Box 85167, 3508 AD Utrecht, The Netherlands.
E-mail:p.crous@westerdijkinstitute.nl
48
Table 1. (Connued).
Current name Basionym Specimen Specimen status Year Collected Host Locale Cox2 sequence 28S rDNA
sequence
References
Peronosclerospora
spontanea (W. Weston) C.G.
Shaw
Sclerospora
spontanea W.
Weston
BPI 187043 Lectotype 1919 Saccharum
spontaneum
Philippines, Los Banos — — Weston (1921),
this paper
BPI 187073 Isotype 1919 Saccharum
spontaneum
Philippines, Los Banos — — Weston (1921),
this paper
Peronosclerospora westonii
J.A. Crouch & Thines
Illustraon Holotype 1961 Iseilema
prostratum
India, Poona — — Srinivasan et al.
(1961), this paper
Poakatesthia pennise (R.G.
Kenneth & J. Kranz) Thines &
Göker
Plasmopara
pennise R. G.
Kenneth & Kranz
IMI 137328c Holotype 1968 Pennisetum
glaucum
Ethiopia, Bako/Shoa EF426475 — Thines & Göker
(2007)
Sclerophthora cryophila W.
Jones
DAOM
20643
Holotype 1948 Dactylis
glomerata
Canada, Brish
Columbia
— — Jones (1955), this
paper
Sclerophthora lolii J.A.
Crouch & Thines
Illustraon Holotype 1964 Lolium rigidum Israel, Mikve — — Kenneth (1964),
this paper
Sclerophthora macrospora
(Sacc.) Thirum. et al.
Sclerospora
macrospora Sacc.
BPI 187265 Neotype 1895 Phlaris
arundinaceae
Germany, Saxony,
Königstein
— — This paper
BPI 187266 Isotype 1895 Phlaris
arundinaceae
Germany, Saxony,
Königstein
— — This paper
HUH 892 Voucher Zea mays China KP965748 EU826119 Choi et al. (2015)
Sclerophthora rayssiae J.A.
Crouch & Thines
Illustraon Holotype 1964 Hordeum vulgare Israel, Valley of
Esdraelon
— — Kenneth et al.
(1964), this paper
Sclerophthora zeae J.A.
Crouch & Thines
HCIO 29038 Holotype 1965 Zea mays India, Pantnagar — — Payak & Renfro
(1967), this paper
Sclerospora farlowii Griths BPI 187077 Lectotype 1900 Chloris virgata United States of
America, Arizona
— — Griths (1907),
this paper
BPI 187076 Isotype 1900 Chloris virgata United States of
America, Arizona
Griths (1907),
this paper
BPI 187078 Isotype 1900 Chloris virgata United States of
America, Arizona
Griths (1907),
this paper
FH 965329 Isotype 1900 Chloris virgata United States of
America, Arizona
Griths (1907),
this paper
FH 1093687 Isotype 1900 Chloris virgata United States of
America, Arizona
Griths (1907),
this paper
Sclerospora graminicola
(Sacc.) J. Schröt.
Protomyces
graminicola Sacc.
Schneider
5532
Holotype 1886? Setaria viridis Poland: Legnica
(Liegnitz), Waldau
Schröeter (1886)
HV532 Voucher Pennisetum
glaucum
India, Gulbarga,
Karnataka
DQ365768 AY035514,
AY273987
Nayaka et al.
(2017)

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Graminicolous downy mildew pathogens
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49
Table 1. (Connued).
Current name Basionym Specimen Specimen status Year Collected Host Locale Cox2 sequence 28S rDNA
sequence
References
Sclerospora iseilemas
Thirum. & Naras.
BPI 187262 Lectotype 1947 Iseilema
prostratum
India, Mysore OK185342 OK255493 Thirumalachar
& Narasimhan
(1949), this paper
IMI 38399 Isotype 1947 Iseilema
prostratum
India, Mysore — — Thirumalachar
& Narasimhan
(1949), this paper
Sclerospora northii W.
Weston
BPI 187307 Lectotype 1924 Saccharum
maximum
Fiji Islands, Suva — — Weston (1929),
this paper
FH 965380 Isotype 1924 Saccharum
maximum
Fiji Islands, Suva — — Weston (1929),
this paper
Sclerospora secalina Naumov Not
designated
— 1949? Secale cereale Former U.S.S.R. — — Naumov (1949)
Viennoa oplismeni J.A.
Crouch & Thines
GZU 335974 Holotype 1963 Oplismeni
hirtellus
Guinea, near Kindia — AY035527,
AY273977
Göker et al.
(2003), this paper
IMI 103944 Isotype 1963 Oplismeni
hirtellus
Guinea, near Kindia — — Göker et al.
(2003), this paper
BPI 784624 Isotype 1963 Oplismeni
hirtellus
Guinea, near Kindia — — Göker et al.
(2003), this paper
1 Stevens Philippine Fungi, Island of Luzon, No. 811.
2 Herbarium Schlesischer Pilze: W. G. Schneider, No. 553.

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50
for accessions that were associated with specimens lodged
in reference collecons and described in peer-reviewed
literature. “Unpublished” NCBI nucleode accessions with
uncertain provenance and/or lacking associaon with a peer-
reviewed scienc publicaon were not included in the
summary. New cox2 and 28S rDNA sequence data was extracted
from unpublished genome assemblies of three species:
Peronosclerospora philippinensis, Sclerospora iseilemas,
and Sclerospora northii. Genome data was generated using
Illumina sequencing technology following the general protocols
described in Fletcher et al. (2018); a full paper describing these
genomes is forthcoming.
RESULTS
Including the six species described as part of this paper for
validaon purposes (see Taxonomy secon, below), there are 39
disnct and validly published species that cause downy mildew
diseases of Poaceae hosts. Three subfamilies in the Poaceae, the
warm season (C4 photosynthesis) grass subfamilies Chlorioideae,
Panicoideae, and the cool-season (C3 photosynthesis) grass
subfamily Pooideae, are parasized by these organisms. With the
notable excepon of the widespread pathogen Sclerophthora
macrospora, all the most destrucve, widespread, and
economically important GDM pathogens parasize cereals and
other grasses in the Panicoideae. In contrast with the pathogens
of the Panicoideae, the GDM species known from Chlorideae
hosts (Baobabopsis donbarre, Baobabopsis enneapogonis,
Eraphthora butleri, Sclerophthora farlowii) have rarely been
reported or were reported just once at the me of the original
descripons.
The species Sclerospora magnusiana (Sorokine 1889) is an
uncertain member of the genus Sclerospora, given that its host –
the spore-forming horsetail plant [Equisetum sp. (Equisetaceae,
Pterdophytes)] – is not a member of Poaceae. Waterhouse
(1964) suggested that the species might be a chytrid rather than
a member of Sclerospora, but Sorokine’s (1889) descripon
and depicon of the formaon of oospores appear to depict
an oomycete. However, unlike Sclerospora graminicola, which
produces oospores embedded in the host ssue, the mature
oospores of Sclerospora magnusiana form a powder-like layer
on the infected plants (Sorokine 1889). Sorokine did not specify
a type, but LEP contains a specimen (LEP 9584) collected by N.
Sorokine on Equisetum arvense from Orsk, Russia in 1894 that
could serve as neotype for the species and should be examined,
especially using molecular data. However, as Sclerospora
magnusiana does not infect a grass, it is not included in our
summary.
Taxonomy
Baobabopsis R.G. Shivas et al., IMA Fungus 6: 484. 2015.
Type species: Baobabopsis donbarrei R.G. Shivas et al., IMA
Fungus 6: 485. 2015.
Descripon: Sporangiophores evanescent, hyaline, cylindrical,
75–120 μm × 20–28 μm wide, unbranched, with 5–20
ampulliform to lageniform ulmate branchlets. Sporangia
hyaline, deciduous. Oogonia subglobose, golden yellow, 27–45
× 25–39 μm; wall (including warts) uneven, verrucose with
rounded warts, 3–11 μm thick. Oospores globose to broadly
ellipsoidal, pale to golden yellow, 19–29 × 18–28 μm, one per
oogonium; wall even, smooth, 1–3 μm thick (Thines et al. 2015).
Diagnosis: Baobabopsis is disnguished from all other
Peronosporaceae genera in that it produces broad club-shaped
to cylindrical sporangiophores bearing a cluster of terminal
ampulliform projecons that give rise to sporangia. The genus
is also disnguished through its posion in phylogenec trees
constructed using 28S rDNA and cox2 sequence data.
Note: Baobabopsis currently contains three species and is
exclusively known from Australia as a parasite of Chloridoideae
hosts (Thines et al. 2015, Ryley et al. 2021).
Baobabopsis donbarrei R.G. Shivas et al., IMA Fungus 6: 485.
2015.
Typus: Australia, Western Australia, Kununurra, near Lake Kununurra,
Peros rara (Chloridoideae, Cynodonteae), 19 Apr. 2011, R.G. Shivas &
T.Y. Chi (holotype BRIP 54675).
Descripon: Sporangiophores cylindrical, evanescent, hyaline,
75–120 × 20–28 μm, with 5–20 terminal ampulliform to
lageniform branches with a narrow neck 7–14 × 3–7 μm.
Sporangia broadly ellipsoidal, hyaline, narrowed slightly
approaching base, 16–20 × 11–18 μm. Oogonia subglobose,
golden yellow, (27–)32.5–36.0–39.5(–45) × (25–)28–31.7–36(–
39) μm diam; wall (including warts) uneven, densely verrucose
with rounded warts, 3–9 μm thick. Oospores globose to broadly
ellipsoidal subhyaline to golden yellow, (19–)22–24.1–27(–29)
× (18–)20–22.5–25(–28) μm diam; wall smooth, even, 1–3 μm
thick (Thines et al. 2015; Fig. 1A).
Diagnosis: Produces broad club-shaped to cylindrical
sporangiophores, a unique feature among the Peronosporaceae.
Diers from Baobabopsis enneapogonis because of its
parasism of Peros rara, the producon of densely verrucose
oogonia walls and its unique cox2 sequence, which shares 98.2
% nucleode identy with Baobabopsis enneapogonis.
Reference sequence data: Ex-holotype nucleode sequences
KT248948 (cox2) and KT248945 (28S rDNA).
Host range: Known only from the type specimen on Peros rara.
Notes: To our knowledge, this species has not been reported
since its descripon in 2015 (Thines et al. 2015). The host
is nave to and widely distributed across Australia, and is
also known from New Guinea, the Philippines, Thailand, and
Vietnam. It is unknown if the range of Baobabopsis donbarrei
extends beyond the type locale or whether the species has any
signicant impact on host populaons.
Baobabopsis enneapogonis Thines et al., IMA Fungus 6: 486.
2015.
Typus: Australia, Northern Territory, East MacDonnel Ranges, near
Corroboree Rock turno, Enneapogon cylindricus (Chloridoideae,
Eragrosdeae), 21 Apr. 2007, A.R. McTaggart, J. Liberato, M.D.E. & R.G.
Shivas (holotype BRIP 49822).

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51
Descripon: Oogonia subglobose, golden yellow, (30–)32.5–
36.3–40(–42) × (29–)30–33.1–36(–39) μm; wall moderately
verrucose with rounded warts, 3–11 μm thick (including warts),
uneven, remnants of antheridium oen aached. Oospores
globose to broadly ellipsoidal, pale to golden yellow, (20–) 21.3–
23.0–24.7(–26) × (19–)20.5–21.9–23.5(–24) μm diam; wall even,
smooth, (1–)1.5(–2) μm thick. Asexual morph not observed
(Thines et al. 2015; Fig. 1B).
Diagnosis: Diers from Baobabopsis donbarrei based on (1)
the producon of slightly less prominent warts, and moderately
verrucose oogonial walls; (2) its unique cox2 sequence, which
shares 98.2 % nucleode identy with Baobabopsis donbarrei;
and (3) parasism of Enneapogon avenaceus and Enneapogon
cylindricus. Diers from Baobabopsis marneyi based on its
unique cox2 sequence, which shares 96 % nucleode identy.
Reference sequence data: Ex-holotype nucleode sequence
KT248946 (cox2).
Host range: Enneapogon avenaceus, Enneapogon cylindricus
(Chloridoideae, Eragrosdeae).
Notes: Sporangiophores have not been observed from
Baobabopsis enneapogonis, so it is unknown whether this
species shares the diagnosc broad club-shaped to cylindrical
sporangiophores observed from Baobabopsis donbarrei.
To our knowledge, this species has not been reported since
its descripon in 2015 when four collecons in Australia were
made between 2007 to 2014 (Thines et al. 2015). Enneapogon
avenaceus and Enneapogon cylindricus are endemic to Australia
but are not known elsewhere in the world. Many members of
the genus Enneapogon are globally distributed; however, it is not
Fig. 1. A. Baobabopsis donbarrei, sporangiophore (le) and oospores in cross-secon, some with antheridia aached (upper right). One oospore
is shown in surface view (arrow). B. Baobabopsis enneapogonis, oospores in cross-secon, some with antheridia aached. One oospore is shown in
surface view (arrow). C. Baobabopsis marneyi, oospores. Illustraons were prepared from published reference images found in Thines et al. (2015)
and Ryley et al. (2022).

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52
known if the host range of Baobabopsis enneapogonis extends
beyond the two reported hosts or if the pathogen is distributed
outside of Australia.
Because Baobabopsis enneapogonis parasizes two of the
same hosts and is similar in appearance to Baobabopsis marneyi,
discriminaon between these species should be conrmed
using cox2 sequence data.
Baobabopsis marneyi R.G. Shivas et al., Mycol. Progr. 21: 300.
2022.
Typus: Australia, Queensland, Georgetown, Enneapogon polyphyllus
(Chloridoideae, Eragrosdeae), 13 Apr. 2019, J. Kruse, A.R. McTaggart,
M.J. Ryley, M.D.E. & R.G. Shivas (holotype BRIP 70341).
Descripon: Oogonia sub-globose to globose, golden brown,
(24–)26–33(–35) μm diam; wall 3–8 μm thick (including warts),
uneven, tuberculate, warts rounded 3–5 × 2–3 μm. Oospores
globose to sub-globose, hyaline, (19–)21–24(–25) μm diam,
adnate with oogonial wall; wall 1–2 μm thick, even, smooth
(Ryley et al. 2021; Fig. 1C).
Diagnosis: Baobabopsis marneyi is disnguished from
other species in the genus Baobabopsis through its unique
cox2 sequence, which shares 92 % nucleode identy with
Baobabopsis donbarrei and 96 % nucleode identy
with Baobabopsis enneapogonis. Diers from Baobabopsis
donbarrei by its parasism of Enneapogon species.
Reference sequence data: Ex-holotype nucleode sequence
OK336436 (cox2).
Host range: Enneapogon avenaceus, Enneapogon cylindricus,
Enneapogon polyphyllus (Chloridoideae, Eragrosdeae).
Notes: Baobabopsis marneyi is recently documented from
collecons made on the foliage of three species of Enneapogon
from three regions of Australia (Ryley et al. 2021). Infecon
results in the blades of grass spling along the vascular strands,
somemes up to 20 cm in length. Given the overlapping
host range and morphology of Baobabopsis marneyi and
Baobabopsis enneapogonis, cox2 sequence data should be used
to discriminate these two species.
Eraphthora Telle & Thines [as ‘Erapthora’], Mycol. Progr. 11:
127. 2012.
Type species: Eraphthora butleri (W. Weston) Telle & Thines,
Mycol. Progr. 11: 127. 2012.
Diagnosis: Similar to Basidiophora and Benua, this species is
unique among all other Peronosporaceae genera in possessing
simple, club shaped sporangiophores. Diers from Basidiophora
and Benua by the producon of evanescent sporangiophores,
oospores with thicker walls, and its parasism of Eragross
(Telle & Thines 2012).
Notes: The genus Eraphthora was established to accommodate
the pathogen originally described as Sclerospora butleri
based on the producon of thick-walled oospores resembling
those of Sclerospora (Weston 1921). Following the discovery
that Sclerospora butleri produces unbranched, club-shaped
sporangiophores and zoospores, these morphological
characters were used to jusfy the transfer of the species
to the genus Basidiophora (Thirumalachar & Whitehead
1952). However, Thirumalachar & Whitehead also noted that
nocturnal sporangiospore producon and host leaf shredding
were not known from Basidiophora and suggested that the
species might represent an intermediate form between
Basidiophora and Sclerospora (Thirumalachar & Whitehead
1952). Subsequent authors rejected placement of Sclerospora
butleri in Basidiophora, arguing that host preference, oogonial
morphology, and the nocturnal producon of evanescent
sporangial structures were beer aligned with the genus
Sclerospora (Kenneth & Kranz 1973, Dick et al. 1984, Barreto
& Dick 1991). In 2012, Telle & Thines erected the new genus
Erapthora based on the unique combinaon of morphological
characters and the cox2 phylogenec disncveness that places
it as the sister lineage of Sclerophthora.
The recent idencaon of two new species of Eraphthora
parasizing Eragross cilianensis (Ryley et al. 2021) introduces a
new complicaon regarding members of the genus Eraphthora.
Although the genus is typied by Eraphthora butleri (Telle
& Thines 2012), the four specimens of this species that were
examined when Eraphthora was erected were later idened as
Eraphthora drenthii (Ryley et al. 2021). The two newly described
species—Eraphthora drenthii and Eraphthora occultata—are
sustanally dierent from generic type Eraphthora butleri,
in that they produce substanally larger oospores, thicker
oospore walls, and produce dierent symptoms in the host
plant (Ryley et al. (2021). Addional molecular phylogenec
research incorporang type materials of Eraphthora butleri is
recommended for further claricaon of how these organisms
are related to one another.
Eraphthora butleri (W. Weston) Telle & Thines, Mycol. Progr. 11:
127. 2012.
Basionym: Sclerospora butleri W. Weston, Phytopathol. 21: 125.
1933.
Synonyms: Basidiophora butleri (W. Weston) Thirum. & M. D.
Whitehead Amer. J. Bot. 39: 4. 1952.
‘Sclerophthora butleri’ (W. Weston) M. W. Dick, Straminipilous
Fungi (Dordrecht): 147. 2001. [nom. inval., presumably lapsus
calami (Telle & Thines 2012)].
Typus: Malawi (formerly Nyasaland), Bulaki, Evans tobacco estate,
Eragross aspera (Chloridoideae, Eragrosdeae), Mar. 1927, E. J. Butler
[lectotype designated here, BPI 187075 (MBT 10002143); isotype
designated here, FH 965376 (MBT 10002144)]. Supplementary Fig. S1
shows the lectotype BPI 187075.
Descripon: Oogonia spherical to irregularly subspherical,
pallid golden to dark amber, 33–36.9 µm (up to 29–40.9 μm)
diam, contents comprising a nely granular, hyaline or grayish
matrix, with one or several oil droplets not arranged in any
denite paern; wall relavely even with numerous bluntly
rounded, papillate to nger-like protrusions, 4–10 μm (excluding
protrusions), protrusions hyaline, base 2–4 × 2–5 μm high.
Oospores spherical, hyaline, 19–22.9 μm diam; wall 2–3 μm
thick. Asexual morph not observed (Weston 1933; Fig. 2A).
Diagnosis: Except for Basidiophora and Benua, diers from
all Peronosporaceae by its simple, unbranched, club-shaped
sporangiophores. Diers from Basidiophora and Benua by

© 2022 Westerdijk Fungal Biodiversity Instute
Graminicolous downy mildew pathogens
Editor-in-Chief
Prof. dr P.W. Crous,Westerdijk Fungal BiodiversityInstitute, P.O. Box 85167, 3508 AD Utrecht, The Netherlands.
E-mail:p.crous@westerdijkinstitute.nl
53
its parasism of Eragross spp., thick-walled oospores and
tuberculate oogonial wall, and nocturnal producon of
evanescent sporangiophores. Eraphthora butleri is disnguished
from Eraphthora drenthii and Eraphthora occultata based
on having smaller oospores, thinner oospore walls, and the
symptoms produced in the parasized host.
Reference sequence data: No sequence data available from type
material or bona de specimens.
Host range: Eragross aspera. Also reported from Eragross
amabilis and Eragross tremula (Chloridoideae, Eragrosdeae).
Fig. 2. A. Eraphthora butleri, sporangiophore and oospores in cross secons with antheridia aached. One oospore is shown in surface view (arrow).
B. Eraphthora drenthii, oospores. C. Eraphthora occultata, oospores. D. Graminivora graminicola, sporangiophore and helical haustoria (arrow).
Illustraons were prepared from published reference images found in Weston (1933), Thirumalchar & Whitehead (1952), Thines & Göker (2006) and
Ryley et al. (2022).

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E-mail:p.crous@westerdijkinstitute.nl
54
Notes: Eraphthora butleri is reported on weedy species of
Eragross from Africa, Australia, India, and Italy (Weston 1921,
1933, Patel 1949, Waterhouse 1964, Telle & Thines 2012, Farr
& Rossman 2021). The type host, Eragross aspera, is a weedy
grass distributed throughout Africa, India, and Malaysia in
temperate and tropical regions. Natural infecons of Eragross
aspera by Eraphthora butleri result in disease symptoms such as
chlorosis and malformed, shredded leaves (Weston 1921, 1933,
Patel 1949, Telle & Thines 2012). As noted by Telle & Thines
(2012) it is unknown whether Eraphthora butleri can infect
agronomic species of Eragross such as Eragross tef (te).
Reports prior to 2021 show Eragross cilianensis as a
host of Eraphthora butleri, but new research shows that
downy mildew on this host is aributable to at least two new
species, Eraphthora drenthii and Eraphthora occultata but is
not known from Eraphthora butleri (Ryley et al. 2021). To our
knowledge, nucleode sequence data from bona de specimens
of Eraphthora butleri are not currently available. Nucleode
sequences from specimens previously accepted as Eraphthora
butleri parasizing Eragros cilianensis are now known to
be Eraphthora drenthii (DAR 4201: HQ413338; DAR 4200:
HQ413337; DAR 4288: HQ413339; FR-0046004: HQ413336,
KP965746, KT248944) (Ryley et al. 2021).
Weston did not designate a holotype, but specimens were
accessioned at BPI and FH (BPI 187075, FH 965376). These
specimens bear the published collecon details and are
annotated in Weston’s handwring; BPI 187075 is designated
here as the lectotype for Eraphthora butleri.
Eraphthora drenthii M.J. Ryley et al., Mycol. Progr. 21: 301.
2022.
Typus: Australia, New South Wales, Eragross cilianensis (Chloridoideae,
Eragrosdeae), Apr. 1950, P. Valder (holotype DAR 4201).
Descripon: Oogonia globose to subglobose, light golden,
(64–)68–84(–92) μm diam; wall uneven, 4–7 × 2–3 μm, with
subhyaline, digitate, straight to curved projecons measuring
7–8 μm thick. Oospores globose to sub-globose, (52–)56–67(–
73) μm diam, adnate with oogonial wall, oen with a single
central vacuole; wall even, smooth 6–8 μm thick (Ryley et al.
2021; Fig. 2B).
Diagnosis: Diers from Eraphthora butleri on the basis of having
larger oospores, thicker oospore walls, symptoms induced in
the host, and parasism of Eragross cilianensis. Diers from
Eraphthora drenthii based on nucleode sequence of the Cox2
marker. Diers from Eraphthora occultata based on nucleode
sequence of the Cox2 marker.
Reference sequence data: Ex-holotype nucleode sequence
HQ413338 (cox2).
Host range: Known only from the type host Eragross cilianensis.
Notes: The type host, Eragross cilianensis, is naturalized
through most parts of the world, including Europe, Asia,
Africa and North America. It is not yet known if Eraphthora
drenthi is co-distributed with the host. To date, Eraphthora
cilianensis is only known from from four specimens of Eragross
cilianensis collected during the 1950s in Australia and from an
unidened species of Eragross collected in Italy. Unlike the
generic type Eraphthora butleri, which induces leaf fraying in
its hosts, Eraphthora drenthii parassm results in malformed
inorescences (Ryley et al. 2021).
Eraphthora occultata Y.P. Tan et al., Mycol. Progr. 21: 303. 2022.
Typus: Australia, New South Wales, Warren, Eragross cilianensis
(Chloridoideae, Eragrosdeae), Jan. 1967, K. Brennan (holotype DAR
16237).
Descripon: Oogonia globose to subglobose, light golden, (65–)
71–90(–95) µm diam; wall uneven, 4–10 µm, with straight to
curved, sub-hyaline, digitate projecons measuring 4–7 × 3
µm thick. Oospores globose to sub-globose, (57–)60–71(–75)
µm diam, adnate with oogonial wall, oen with a single central
vacuole; wall even, smooth, 5–6 µm thick. Asexual morph not
observed (Ryley et al. 2021; Fig. 2C).
Diagnosis: Diers from Eraphthora butleri on the basis of having
larger oospores, thicker oospore walls, symptoms induced in
the host, and parasism of Eragross cilianensis. Diers from
Eraphthora drenthii based on nucleode sequence of the Cox2
marker.
Reference sequence data: Ex-holotype nucleode sequence
OK392240 (cox2).
Host range: Known only from the type specimen on Eragross
cilianensis.
Notes: Eraphthora occultata shares many features in common
with its sister species, Eraphthora cilianensis, including
morphology and parasism of Eragross cilianensis. However, it
has only been observed once from the type collecon made in
Australia in 1967.
Graminivora Thines & Göker, Mycol. Res. 110: 651. 2006.
Type species: Graminivora graminicola (Naumov) Thines &
Göker, Mycol. Res. 110: 652. 2006.
Diagnosis: Diers from all other Peronosporaceae through
dierences in haustorium morphology, sporangiophore
morphology and ultrastructure, and nucleode sequences of
rDNA.
Notes: The genus Graminivora, typied by Graminivora
graminicola, was erected to accommodate the pathogen
originally described as Bremia graminicola. The species was
originally described as a Bremia based on features that were
thought to be unique to the genus during the early 20th century.
Specically, Bremia graminicola produces lasng, dichotomously
branched sporangiophores with inated ends, mulple
sterigmata and subglobose sporangia (Naumov 1913). Thines
& Göker (2006) documented dierences in haustorium and
sporangiophore morphology and 28S rDNA sequences between
the Bremia generic type and Bremia graminicola, resulng in the
transfer of Bremia graminicola into the new genus Graminivora.
Graminivora contains one species and is distributed in four Asian
countries as a parasite of Arthraxon hispidus.

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Graminicolous downy mildew pathogens
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E-mail:p.crous@westerdijkinstitute.nl
55
Graminivora graminicola (Naumov) Thines & Göker, Mycol. Res.
110: 652. 2006.
Basionym: Bremia graminicola Naumov, Bull. Soc. Mycol. France
29: 275. 1913.
Synonym: Bremia graminicola var. indica Patel, Indian
Phytopathol. 1: 106. 1949.
Typus: Russia, South Ussuriysk region, Siberia, Arthraxon hispidus
(Panicoideae, Andropogoneae), 31 Jul. 1912, N. Naumov (lectotype
designated here LEP 4385 [MBT 10002145]; isotypes BPI 786232,
LEP 4377, LEP 4384, FH 01012075, E 00297399 [MBT 10002146]).
Supplementary Fig. S2 shows the lectotype BPI 786232.
Descripon: Sporangiophores hyaline with inated base above
stomata; curved, dichotomous or irregular branching in the
upper part, usually 4–6 mes, aer the last ramicaon inated
into a vesicle carrying four ulmate branchlets (somemes two,
as many as eight, typically in even numbers), up to 600 μm long
× 9–10 μm wide at the base and 5–6 μm wide in the terminal
ramicaons. Sporangia globose to ovoid, hyaline, average diam
12 μm, with short basal and papilla at the slightly aened apical
end, mode of germinaon unknown. Oospores not observed
(Naumov 1913, Thines et al. 2006; Fig. 2D).
Diagnosis: Diers from Bremia species in that it parasizes
Arthraxon hispidus, and produces hyphal haustoria that oen
form small spirals, with sporangiophores that usually show
strong curving from the very start of ramicaons, and swollen
sporangiophore ps that typically carry 2–4 ulmate branchlets.
Diers from other Peronosporaceae on the basis of lasng,
dichotomously branched sporangiophores with inated ends
and its phylogenec posion based on cox2 and 28S rDNA
sequences.
Reference sequence data: Sequence data not available from
type materials. Ex-HUH 738 nucleode sequences KP965747
(cox2), KP965742 (28S rDNA).
Host range: Known only from the type host Arthraxon hispidus.
Notes: Graminivora graminicola is known only from Arthraxon
hispidus from China, India, Japan, and Russia (Togashi 1926, Ito
1936, Patel 1949, Novotel’nova & Pysna 1985, Tao 1998, Thines
& Göker 2006). Parasized leaves are discolored with variably
sized yellow to reddish spots, oen running parallel to the leaf
veins, with leaves eventually withering and dying (Naumov
1913). The type host – a weedy grass commonly known as small
carpetgrass—is nave to the Asian connent where Graminivora
graminicola has been reported. It is unknown if Graminivora
graminicola also resides in North America, where Arthraxon
hispidus is present as a highly invasive species thought to have
been introduced to the connent in 1876. Although Arthraxon
hispidus is widely distributed worldwide, there is no indicaon
of any economic or ecological impact on the host when infected
by this pathogen.
The Harvard Herbarium database lists the collecon locaon
of FH 01012075 as “Liberia, Africa,” which appears to be a
misreading of Naumov’s handwring. On the digized version
of the specimen label for FH 01012075 (hp://storage.idigbio.
org//mycology/barcode-01012/FH01012075.jpg), one can
see the ambiguity of the rst leer (L/S) of the locaon. Naumov
(1913) lists the locaon as “aux environs de Wladiwostok” and
“Austro-Ussuriensi (Rossiae orient.),” which roughly translates
to “around Wladiwostok” and “Ussurijsk region of eastern
Russia.” Both fall within the broad geographic area known
as “Siberia”; therefore, “Liberia” is incorrect. Similarly, the
online database of the Royal Botanical Garden of Edinburgh
lists the locaon of E 00297399 as “Jaczewski, Poland,” which
is also an error in digizing the specimen label. Both the FH
and BPI specimens originated from “Herbario Instu Mycol.
et Phytopath. Jaczewski Petropolis,” which is the former name
of LEP. Assuming LEP also sent E their specimen, it seems likely
“Jaczewski Petropolis” was incorrectly entered as the locaon
of collecon instead of the herbarium from which the material
was sent.
Naumov did not designate a holotype, but materials from the
original collecon were found in BPI, E, FH, and LEP. LEP 4385 is
designated here as the lectotype for Graminivora graminicola.
Peronosclerospora (S. Ito) Hara, in Shirai & Hara, List of Japanese
Fungi hitherto unknown, 3rd Edn: 247 [‘257’]. 1927.
Basionym: Sclerospora subgen. Peronosclerospora S. Ito, Bot.
Mag., Tokyo 27: 218. 1913.
Peronosclerospora (S. Ito) C.G. Shaw, Mycologia 70: 594. 1978.
[nom. illegit., Art. 53.1]
Type species: Peronosclerospora sacchari (T. Miyake) Shirai &
Hara, List of Japanese Fungi hitherto unknown, 3rd edn: 247
[‘257’] (1927).
Descripon: No descripon was provided for the basionym
Sclerospora subgen. Peronosclerospora or by Shirai & Hara when
the genus Peronosclerospora was erected (Ito 1913; Shirai &
Hara 1927). In his superuous descripon of Peronosclerospora,
Shaw (1978) provided a useful descripon of the genus,
as follows: “Mycelium parasic in higher plants, hyaline,
coenocyc; imperfect state like Sclerospora except that conidia
are always produced rather than sporangia. Conidiophores
produced at night, erect, dichotomously branched two to ve
mes; sterigmata conoid to subulate, usually two, but three
or four in some species. Conidia ellipsoid, ovoid or cylindrical,
wall of uniform structure, neither operculate or poroid, always
germinang by a single germ tube. Oogonia subglobose to
spherical. Oospores globose or subglobose, 25–55 μm in diam;
oospore wall parally or completely fused to the wall of the
oogonium, oospore wall of three layers: exosporium chestnut
to reddish brown at maturity, irregularly ridged, 1.0–3.0 μm
thick; mesosporium very thin, hyaline; endosporium hyaline,
uniformly thick, 1.5–3.5 μm thick.”
Notes: The disncon between what we now recognize
as Peronosclerospora and the genus Sclerospora was rst
pointed out by Ito (1913), who split Sclerospora into two
subgenera based on dierences in asexual spore germinaon,
which occurs directly by germ tubes in Peronosclerospora
and indirectly by zoospores in Sclerospora. Ito recognized
that two taxa would fall into the new subgenus Sclerospora
subgen. Peronosclerospora; namely Sclerospora sacchari and
Sclerospora graminicola var. andropogonis-sorghi (Ito 1913).
Sclerospora subgen. Peronosclerospora was described as the
genus Peronosclerospora in 1927 (Shirai & Hara 1927), with
just one species (Peronosclerospora sacchari) transferred as
the generic type (Shirai & Hara 1927). The original descripon
of Peronosclerospora went unnoced among some members of

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Crouch et al.
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Prof. dr P.W. Crous,Westerdijk Fungal BiodiversityInstitute, P.O. Box 85167, 3508 AD Utrecht, The Netherlands.
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56
the scienc community, resulng in the descripon of several
non-zoosporic species in the genus Sclerospora rather than in
Peronosclerospora (Sclerospora dichanthiicola, Sclerospora
philippinensis, Sclerospora sorghii, Sclerospora westonii), and
a second, superuous descripon of the genus in 1978 (Shaw
1978, Shaw & Waterhouse 1980).
From a praccal standpoint, discriminang between
Peronosclerospora and Sclerospora based on dierences in
asexual structures is not a trivial maer. Development of asexual
spores by members of both genera is nocturnal under natural
condions. In Peronosclerospora, structures persist for just a few
hours in the early morning unl they germinate under conducive
environmental condions (e.g., Sriinivasan et al. 1961). Aer
germinaon, the asexual spores and related structures rapidly
collapse, leaving no trace behind. As a result, asexual structures
are not well preserved on herbarium materials and other
collecons on non-living host material, hindering idencaon
and taxonomic study. Structures of Sclerospora last longer, but
within a few days can also vanish. The challenging applicaon of
asexual spore morphology for Peronosclerospora idencaon
is further complicated by the impact of environmental eects,
such as host species, variety, and climate, on spore size and
shape (Delanie 1972, Leu 1973, Kimigafukuro 1979, Bock et al.
2000, Dudka et al. 2007, Runge & Thines 2011).
Peronosclerospora currently includes 12 species that are
parasites of hosts in the subfamily Andropogoneae, including
destrucve pathogens of staple crops such as maize, sorghum,
and sugarcane. The genus is widely distributed across the eastern
hemisphere, including Africa, Australia, East Asia, and Oceania.
Just one species of Peronosclerospora – Peronosclerospora
sorghi – is well documented from the Western Hemisphere,
following its introducon to Central America in the 1950s
(Toler et al. 1959, Furell 1974, Frederickson & Renfro 1977).
Peronosclerospora eriochloae (as Peronosclerospora globosa)
was reported from Texas in a meeng abstract (Kubicek &
Kenneth 1984), however those reports need further scruny to
verify the identy of the pathogen.
Peronosclerospora arisdae J. Kruse et al., Mycol. Progr. 21:
303. 2022.
Typus: Australia, Queensland, in leaves of Arisda hygrometrica
(Poales, Poaceae), 27 Apr. 2018, J. Kruse, M.J. Ryley, S.M. Thompson,
M.D.E. & R.G. Shivas (holotype BRIP 67069).
Descripon: Oogonia globose to sub-globose, golden yellow,
(30–)39–51(–53) μm diam; wall with sparse, low, irregular,
truncate ridges, 6–14 μm thick. Oospores globose to sub-
globose, golden yellow, (23–)27–31(–32) μm diam, adnate with
oogonal wall, with a single vacuole; wall even, smooth, hyaline,
1–2 μm thick. Asexual morph not observed (Ryley et al., Fig. 3A).
Diagnosis: Diers from all other Peronosclerospora based on
oogonial walls with irregular, low, truncate ridges, parasisim
of Arisda hygrometrica, and its phylogenec posion based on
the cox2 nucleode sequences.
Reference sequence data: Ex-holotype nucleode sequence
OK336438 (cox2).
Host range: Known only from the type specimen on Arisda
hygrometrica.
Notes: The host of Peronosclerospora arisdae, Arisda
hygrometrica, is an Australian nave grass, and the only known
member of the the subfamily Arisdoide associated with a
downy mildew. Infecon by Peronosclerospora arisdae results
in spling of the leaf blade into strands that can measure up to
50 cm long.
Peronosclerospora boughtoniae M.J. Ryley et al., Mycol. Progr.
21: 303. 2022.
Typus: Australia, Queensland, Lizard Island, in leaves of Sorghum
plumosum (Poales, Poaceae), 7 May 1978, V.H. Broughton (holotype
BRIP 14388).
Descripon: Oogonia globose to sub-globose, light golden brown,
(25–)29–40(–50) μm in diam; wall smooth with occasional
scabrid, aened sides bordered by inconspicuous ridges, 1–12
μm thick. Oospores globose, hyaline, (22–)24–29(–31) μm diam;
wall even, smooth, 1–2 μm thick. Asexual morph not observed
(Ryley et al., Fig. 3B).
Diagnosis: Diers from Peronosclerospora maydis on the
same host in that it has smaller oospores. Disnguished from
Peronosclerospora mactaggari on Sorghum morense through
its unique cox2 sequence (96 % nucleode identy).
Reference sequence data: Ex-holotype nucleode sequence
OK33649 (cox2).
Host range: Known only from the type specimen on Sorghum
plumosum.
Notes: Infecon by Peronosclerospora boughtoniae results in
spling of the leaf blade into strands that can measure up to
15 cm long.
Peronosclerospora dichanthiicola (Thirum. & Naras.) C.G. Shaw,
Mycologia 70: 595. 1978.
Synonym: Sclerospora dichanthiicola Thirum. & Naras. [as
ʻdichanthicolaʻ], Phytopathol. 42: 598. 1952.
Typus: Illustraon in Phytopathol. 42: 597, g. 1, 1952 (lectotype
designated here [MBT 10002147]) based on collecon made in
India, Bihar, in the culms of Dichanthium annulatum (Panicoideae,
Andropogoneae), 18 Dec. 1951, M. J. Thirumalachar.
Descripon: Conidiophores evanescent, nocturnal, erect, 83–
130 μm long × 13 μm wide at basal plug, 17–27 μm wide at main
axis branching point; basal part isodiametric, 33 × 13 μm width
with inconspicuous knob-like structure at the base; branches
are dichotomous (rarely secondary and terary branches), 2–6
in number, 33–37 × 83–90 μm, usually with primary branches
that give rise to 2–3 obconical tapering sterigmata with conidia.
Conidia globose to obovoid, hyaline, thin-walled, 21–28 ×
15–18 μm, germinang by germ tubes. Oospores unknown
(Thirumalachar et al. 1952; Fig. 3D).
Reference sequence data: No sequence data available.
Host range: Known only from the type specimen on Dichanthium
annulatum.

© 2022 Westerdijk Fungal Biodiversity Instute
Graminicolous downy mildew pathogens
Editor-in-Chief
Prof. dr P.W. Crous,Westerdijk Fungal BiodiversityInstitute, P.O. Box 85167, 3508 AD Utrecht, The Netherlands.
E-mail:p.crous@westerdijkinstitute.nl
57
Notes: To our knowledge, reports of Peronosclerospora
dichanthiicola are limited to a single observaon on
Dichanthium annulatum, an important perennial forage grass
in India (Waterhouse 1964, Thirumalachar & Narasimhan
1952, Farr & Rossman 2021). Dichanthium annulatum infected
with Peronosclerospora dichanthiicola exhibits leaves that are
chloroc with yellow streaks, but there is no indicaon as to the
overall impact of the pathogen on plant health (Thirumalachar
& Narasimhan 1952). Given the rarity of Peronosclerospora
dichanthiicola and its inability to infect maize or sorghum
Fig. 3. A. Peronosclerospora arisdae, oospores in cross-secon and one in surface view (arrow). B. Peronosclerospora boughtoniae, oospores.
C. Peronosclerospora eriochloae sporangiophore and oospores. D. Peronosclerospora dichanthicola, mature and immature sporangiospores and
germinang sporangia. E. Peronosclerospora heteropogonis, oospores and sporangiophore. Illustraons were prepared from published reference
images in Thirumalachar & Narasimhan (1952), Siradhana et al. (1980), Ryley & Langdon (2001) and Ryley et al. (2022).

© 2022 Westerdijk Fungal Biodiversity Instute
Crouch et al.
Editor-in-Chief
Prof. dr P.W. Crous,Westerdijk Fungal BiodiversityInstitute, P.O. Box 85167, 3508 AD Utrecht, The Netherlands.
E-mail:p.crous@westerdijkinstitute.nl
58
(Thirumalachar & Narasimhan 1952), the pathogen appears
have lile to no discernable impact on culvated crops.
The species was described from material collected from
India in 1951, but a type was not formally designated and it is
unknown whether any materials from the study of Thirumalachar
& Narasimhan (1952) were preserved in a reference collecon.
Although oospores were not observed, the asexual morph
was well documented in the original publicaon, therefore an
illustraon from that publicaon is ulized as the lectotype.
Peronosclerospora eriochloae Ryley & Langdon, Mycotaxon 79:
89. 2001.
Typus: Australia, Upper Pilton, Queensland, on llers of Eriochloa
pseudoacrotricha (Panicoideae, Paniceae), 9 Apr. 1979, M.J. Ryley
[holotype BRIP 13693; isotypes BRIP 13691, BRIP 13692, FR-0046005
(MBT 10002148)].
Descripon: Conidiophores hyaline, 245–280 μm long with
septum 90–115 μm above base; swollen base 6–13 μm wide
decreasing to 6–9 μm wide at septum; above septum diam
increases to 20–30 μm at the start of branching; dichotomously
branched with secondary, terary, and quaternary branches 45–
100 μm wide; sterigmata at ps of branches, conoid-subulate
4–9 μm long × 3–4 μm wide. Conidia globose to subglobose
hyaline, (9–)13.3(–18) × (9–)12(–13.4) μm, without operculum
or pore; germinang by one or two germ tubes. Oogonium
globose to subglobose, orange to luteus, (33–)46.6(–70) μm
diam; wall hyaline, conuent with oospore wall, 1.0–1.5 μm
thick. Oospores globose, hyaline, 27–33.5(–46) μm diam, one
per oogonium; wall in two layers with exosporium reddish
brown, 2–15 μm thick; and endosporium hyaline, 2–3 μm thick.
(Ryley & Langdon 2001; Fig. 3C).
Reference sequence data: Ex-isotype FR-0046005 nucleode
sequences HQ261813 (cox2), HQ261786 (28S rDNA).
Host range: Eriochloa pseudoacrotricha, Eriochloa laevinode,
Zea mays (Panicoideae, Andropogoneae).
Notes: Peronosclerospora eriochloae has been idened from
three hosts in Australia (Ryley & Langdon 2001, Telle et al. 2011),
but it is unknown if the pathogen is distributed outside of that
country. Eriochloa pseudoacrotricha is nave to and widely
distributed in Australia but also has been introduced across the
southern USA (Texas) and South America. Based on similaries
in morphological characteriscs, Ryley & Langdon (2001)
hypothesized that the invalidly published Peronosclerospora
globosa described from Eriochloa contracta in Texas (Kubicek
& Kenneth 1984) might represent the same species as
Peronosclerospora eriochloae; see notes on Peronosclerospora
globosa below.
The impact of Peronosclerospora eriochloae on host
populaons is not known. Infecon of Eriochloa pseudoacrotricha
results in llers that do not produce inorescences, and
abnormally wide, chloroc frayed leaves that eventually become
necroc (Ryley & Langdon 2001).
‘Peronosclerospora globosa’ Kubicek & R.G. Kenneth,
Phytopathol. 74: 792. 1984. [nom. nud, Art. 36.1, 39.1]
Typus: non designates.
Notes: Reported on Eriochloa contracta from the southern USA
(Texas) and on Eriochloa creba (Panicoideae, Paniceae) from
New South Wales, Australia (Kubicek & Kenneth 1984). Kubicek
& Kenneth (1984) proposed the name Peronosclerospora
globosa along with a short English descripon in a meeng
abstract but never eecvely published a Lan descripon
or designated a holotype (Ryley & Langdon 2001). Based on
morphology, Ryley & Langdon (2001) found their specimen of
Peronosclerospora eriochloae on Eriochloa pseudoacrotricha
similar to Peronosclerospora globosa, but deemed it suciently
dierent to describe it as a new species rather than validate
Peronosclerospora globosa. If specimens from the Texas
collecons referred to in Kubicek & Kenneth (1984) can be
located, they should be further examined to see if they represent
a disnct species. However, it is unknown if Kenneth’s collecons
are extant, as a search of Mycoportal, BPI, and TAMU did not
yield any specimens corresponding to the Texas collecon.
Peronosclerospora heteropogonis J.A. Crouch sp. nov.
MycoBank MB 840573.
Synonym: ‘Peronosclerospora heteropogonis’ Siradhana et al. [as
‘heteropogoni’] Curr. Sci. 49: 316. 1980. [nom. inval., Art. 40.1].
Typus: India, Rajasthan, Udaipur, Sisarma, on leaves of Zea mays
(Panicoideae, Andropogoneae), 2005, K. Mathur (holotype designated
here, HOH 898).
Descripon: Conidiophores evanescent, nocturnal, erect, with
dichotomous branching and secondary and terary branches
with a swollen base; from base to branching 81.6–142.8 ×
14.3–255.5 μm with an average of 101.8 × 20.1 μm. Conidia
globose, hyaline, thin-walled without operculum or pore, 14.3–
22.4 × 14.3–20.4 (17.7 × 16.2) μm; germinaon by germ tubes.
Oospores globose, tuberculate, persistent, 24.5–36.7 (29.0)
μm diam, mostly fused to oogonial wall, contents granular,
germinaon by zoospores (Siradhana et al. 1980; Fig. 3E).
Diagnosis: Similar morphology as Peronosclerospora sorghi
but diers by its inability to infect sorghum and in oospore
morphology, with Peronosclerospora heteropogonis producing
tuberculate oospores and Peronosclerospora sorghi producing
oospores that have an irregularly polygonally-angled
ornamentaon. Disnct on the basis of the nucleode sequence
of cox2.
Reference sequence data: Ex-holotype nucleode sequence
EU116054 (cox2).
Host range: Heteropogon contortus, Zea mays (Panicoideae,
Andropogoneae).
Notes: Peronosclerospora heteropogonis causes Rajasthan
downy mildew disease of Heteropogon contortus (spear grass)
and maize on a regional basis in the Udaipur district of the state
of Rajasthan in India (Siradhana et al. 1980, Yen et al. 2004). The
disease can be quite destrucve, leading to leaf chlorosis and
shredding in both hosts, and causing as much as 60–80 % yield
loss in suscepble hybrid corn lines depending on inoculum load
and weather condions (Dange et al. 1973, 1974, Rathore et al.
2002). However, research of this downy mildew is ranked as a
low priority in India based on prevalence, incidence and acreage
aected (Thakur & Mathur 2002).

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59
This species was rst reported as Peronosclerospora sorghi
on Heteropogon contortus (Dange et al. 1973, Siradhana et al.
1980) and later described as Peronosclerospora heteropogonis
based on morphology and the inability to infect sorghum,
which disnguished the species from Peronosclerospora sorghi
(Siradhana et al. 1980). However, Siradhana et al. (1980) did
not designate a holotype, which means that Peronosclerospora
heteropogonis Siradhana et al. was not validly published
(Art. 40.1, Turland et al. 2018). In 2005, Thines et al. (2008)
made a fresh collecon of the pathogen from the Udaipur
region of India from maize (HOH 898), where the original
collecons by Siradhana et al. (1980) were made. Thines et
al. (2008) conrmed the disncveness of HOH 898 from
Peronosclerospora sorghi and other members of the genus
using a molecular phylogenec analysis of cox2; this specimen
is therefore designated the holotype for the newly validated
species.
Peronosclerospora ischaemi M.J. Ryley et al., Mycol. Progr. 21:
304. 2022.
Typus: Australia, Queensland, on leaves of Ischaemum fragile
(Panicoideae, Andropogoneae), 14 Apr. 2019, J. Kruse, A.R. McTaggert,
M.J. Ryley, M.D.E. & R.G. Shivas (holotype BRIP 70369).
Descripon: Oogonia subglobose to irregular, golden brown,
(55−)61−68(−70) × (49−)56−65(−68) μm diam; wall uneven,
aened, smooth, 5−20 μm thick. Oospores globose, hyaline,
(35−)41−48(−50) diam, adnate with oogonium wall, with a single
vacuole; wall μm thick, even, smooth, hyaline, 4−6 μm thick (Fig.
4A). Asexual morph not observed (Ryley et al. 2022).
Diagnosis: Disnct from other Peronosporaceae based on
parasisim of Ischaemum fragile. Disnguished from sister
species Peronosclerospora jamesiae and Peronosclerospora
sehima based on the nucleode sequence of cox2 (98 %
sequence similarity).
Reference sequence data: Ex-holotype nucleode sequence
OK336433 (cox2), OK350683 (28S rDNA).
Host range: Known only from the type specimen on Ischaemum
fragile.
Notes: The host of Peronosclerospora ischaemi, Ischaemum
fragile, a species distributed across parts of Australia and
New Guinea, and is the only known member of the the genus
Ischaemum associated with a downy mildew. Infecon by
Peronosclerospora ischaemi results in spling of the leaf blade
into tangled vascular strands that can measure up to 30 cm long.
Peronosclerospora jamesiae R.G. Shivas et al., Mycol. Progr. 21:
304. 2022.
Typus: Australia, Northern Territory, Wagait Beach, in leaves of
Sorghum intrans (Panicoideae, Andropogoneae), 1 Apr. 2016, R.S.
James (holotype BRIP 65234).
Descripon: Oogonia highly variable shape including sub-
globose, ovoid and cuboid, dark golden brown, (40–)46–60(–80)
μm in diam; wall smooth, rounded to at, occasionally concave,
2–15 μm thick. Oospores sub-globose to ovoid somemes with
a aened side, (30–)32–42(–55) μm diam, with prominent
oil globule; wall hyaline, even, smooth, 1–2 μm thick (Fig. 4B).
Asexual morph not observed (Ryley et al. 2022).
Diagnosis: Diers from other Peronosporaceae on Sorghum
spp. by having larger oospores with a darker oogonial wall.
Dieres from sister species Peronosclerospora ischaemi and
Peronosclerospora sehima based on the nucleode sequence
of cox2 (98 % nucleode similarity) and parasism of Sorghum
intrans.
Reference sequence data: Ex-holotype nucleode sequence
OK336444 (cox2).
Host range: Known only from the type host Sorghum intrans.
Notes: The host of Peronosclerospora jamesiae, Sorghum
intrans, is a wild annual grass species nave to Northern regions
of Australia. Infecon by Peronosclerospora jamesiae results in
spling of the leaf blade into tangled vascular strands that can
measure up to 30 cm long.
Peronosclerospora mactaggari R.G. Shivas et al., Mycol. Progr.
21: 305. 2022.
Typus: Australia, Northern Territory, Dorat Rd., Robins Falls, in leaves
of Sorghum morense (Panicoideae, Andropogoneae), Apr. 2012, A.R.
McTaggart & R.G. Shivas (holotype BRIP 57677).
Descripon: Oogonia sub-globose to globose, light golden
brown, (30–)33–36(–40) μm diam; wall smooth, uneven, 1–8
μm thick. Oospores globose, (23–)25–27(–29) μm diam, with
a single vacuole, adnate with oogonial wall; wall hyaline, even,
smooth 1–2 μm thick. (Fig. 5A). Asexual morph not observed
(Ryley et al. 2022).
Diagnosis: Disnguished from Peronosporaceae causing grass
downy mildews based on the nucleode sequence of cox2,
which shares 96 % similarity with the most closely related taxon,
Peronosclerospora boughtoniae.
Reference sequence data: Ex-holotype nucleode sequence
OK336446 (cox2), OK350687 (28S rDNA).
Host range: Known only from the type specimen on Sorghum
morense.
Notes: Infecon by Peronosclerospora mactaggari results in
spling of the leaf blade into tangled vascular strands that can
measure up to 20 cm long.
Peronosclerospora maydis (Racib.) C.G. Shaw, Mycologia 70:
595. 1978.
Basionym: Peronospora maydis Racib., Ber. Deutsch. Bot. Ges.
15: 475. 1897.
Synonyms: Sclerospora maydis (Racib.) E. J. Butler, Memoirs of
the Dept. Agric. India. Bot. Ser. 5: 275. 1913.
Sclerospora javanica Palm, Meded. Lab. Pl. Ziekt. Buitenz. 32: 18.
1918.
Peronosclerospora australiensis R.G. Shivas et al., Australas. Pl.
Pathol. 41: 126. 2012.

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Crouch et al.
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60
Typus: Indonesia, Java, Jawa Tengah, Tengal, Zea mays (Panicoideae,
Andropogoneae), sine dat. [lectotype KRA O-5859(J); isotypes BPI
789413 (MBT 10002149), in KRAM, and M. Raciborski, Cryptogamae
parasicae in Insula Java Lectae 7]. Supplementary Fig. S3 shows the
isotype BPI 789413.
Descripon: Mycelium coenocyc, intercellular, parasic
throughout host (excluding roots), with many dierenally shaped
haustoria, and two kinds of hypha: straight and sparsely branched,
and lobed and irregularly branched. Conidiophores robust, erect,
200–550 µm high × 20–25 µm wide, with septated basal cells 60–
180 µm long, dichotomously branched 2–4 mes, branchlets with
two or more (generally 3–6) conical sterigmata (6–9 μm long)
each bearing one individual sporangium. Sporangia hyaline, oval
or spherical to subspherical, non-papillate, and 15–18 μm wide,
direct germinaon by 1–2 germ tubes (Raciborski 1897; Fig. 4C).
Sexual structures rare or unknown (Semangoen 1970), that have
been described from the type specimen of what was originally
described as Peronosclerospora australiensis but is now accepted
as a synonym of Peronosclerospora maydis (Suharjo et al. 2020);
that descripon is as follows: Oogonia golden orange to yellowish
or reddish brown, globose, subglobose, broadly ellipsoidal to
irregularly polyangular, 55–76 μm diam; exosporium 2–15 μm
wide, uneven, smooth, convoluted. Oospores one per oogonium,
Fig. 4. A. Peronosclerospora ischaemi, oospores. B. Peronosclerospora jamesiae, oospores. C. Peronosclerospora maydis, sporangiophore, germinang
sporangia, and oospores. D. Peronosclerospora miscanthi, sporangiophore, germinang sporangium, and oospores. E. Peronosclerospora noblei,
sporangiophore, sporangia, and oospores. The top three oogonia are illustrated in surface view, including one oogonium that is one cracked open with
an oospore released from oogonial wall (arrow). Illustraons were prepared from published reference images in Raciborski (1897), Weston (1929,
1942), Chu (1953), Shivas et al. (2012), Widianni et al. (2015) and Ryley et al. (2022).

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Graminicolous downy mildew pathogens
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Prof. dr P.W. Crous,Westerdijk Fungal BiodiversityInstitute, P.O. Box 85167, 3508 AD Utrecht, The Netherlands.
E-mail:p.crous@westerdijkinstitute.nl
61
sub-hyaline to pale yellow, globose or broadly ellipsoidal, 39–55
μm diam, oen with a large vacuole; endosporium 2.5–4.0 μm
wide, even, smooth (Shivas et al. 2012; Fig. 4C).
Diagnosis: Sequence analysis of cox2 has been used
to dierenate Peronosclerospora maydis from other
Peronosclerospora spp. (Suharjo et al. 2020).
Reference sequence data: Ex-lectotype nucleode sequence
MW025835 (cox2).
Host range: Saccharum spontaneum, Sorghum arundinaceum,
Sorghum morense, Zea mays, Zea mexicana, Zea mexicana ×
Zea mays hybrids (Panicoideae, Andropogoneae).
Fig. 5. A. Peronosclerospora mactaggari, oospores. B. Peronosclerospora panici, sporangia and fragments of sporangiophore ps. C.
Peronosclerospora philippinensis, sporangiophores, sporangia (including germinang sporangia), and oospores (including one germinang oospore,
arrow). D. Peronosclerospora sacchari, sporangiophore, sporangia (including germinang sporangia), and oospores. Illustraons were prepared from
published reference images in Miyake (1912), Weston (1920), Acedo & Exconde (1967), Elazegui & Exconde (1968), Singh & Chaube (1968), and
photographs of Peronosclerospora philippinensis provided by Gary Peterson.

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Crouch et al.
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62
Notes: Peronosclerospora maydis is the causal agent of Java
downy mildew and is one of the three most devastang downy
mildew pathogens of maize (Lukman et al. 2016). In Indonesia,
crop damages of 40–100 % have been recorded (Pudjiwa et
al. 2013). Disease symptoms include severe chlorosis in the
upper leaves, stunng, deformaon, and lodging; infecons
by Peronosclerospora maydis may lead to death in suscepble
maize variees (Smith & Renfro 2016). The pathogen is
widely distributed in the tropics of Australia, China, India,
Indonesia, Jamaica, Taiwan, Thailand, and Venezuela. Reports
of Peronosclerospora maydis in the Congo Democrac Republic
and Argenna are considered possible misidencaons
(Semangoen 1970, Kenneth 1976).
Sexual structures are rare or absent under natural or
experimental condions on the type host (Semangoen 1970,
Suharjo et al. 2020), but were described from Sorghum
morense plants in Australia (Shivas et al. 2012). Oospores of
Peronosclerospora maydis infecng maize originally described
by Raciborski (1897) and Rutgers (1916) were later idened
as Pythium spp. and Paramecium spp. (Palm 1918, Semangoen
1970).
Peronosclerospora miscanthi (T. Miyake) C.G. Shaw, Mycologia
70: 596. 1978.
Basionym: Sclerospora miscanthi T. Miyake ex. Troer [as
‘mischanthi’], in Troer, Syll. Fung. (Abellini) 24: 65. 1926.
Typus: Taiwan, Taipei, Miscanthus sinensis var. formosanus, 20 Jul. 1915,
K. Sawada [neotype designated here BPI 187301 (MBT 10002150)].
Supplementary Fig. S4 shows the neotype BPI 187301.
Descripon: Conidiophores 97–300 (up to 438) × 12–37 μm,
branched twice at the p. Conidia elongately ovoid, (37.2–)
41.8(–48.6) × 14.3–22.9 μm (av. 41.8 × 18) μm diam, germinate
directly by a germ tube. Oogonia reddish brown, mostly 58.3–
63.5 × 51.5–56.9 (range 43.2–80 × 33.2–64.8) μm, walls unevenly
thick from 3–8 μm to 12–24 μm thick, with small excrescences.
Oospores 43.5–47.1 μm diam (Miyake 1912, Chu 1953; Fig. 4D).
Reference sequence data: Ex-NY: Stevens Philippine Fungi, Island
of Luzon, No. 811 nucleode sequences HQ261811 (cox2),
HQ261784 (28S rDNA).
Host range: Miscanthus japonicus, Miscanthus sinensis,
Saccharum ocinale, Saccharum robustum, Saccharum
spontaneum (Panicoideae, Andropogoneae).
Notes: Leaf spling downy mildew disease caused by
Peronosclerospora miscanthi was rst idened in 1912
in Taiwan (Miyake 1912). The pathogen was subsequently
reported from several species of Miscanthus and two species of
Saccharum from China, Fiji, New Guinea, the Philippines, and
Taiwan, with most reports of the pathogen presented in the
form of checklists and surveys (Ito & Tokunaga 1935, Chu 1953,
Waterhouse 1964, Telle et al. 2011). Inoculaon experiments
show that Peronosclerospora miscanthi has the ability to
infect maize, but natural infecons of this host are unknown
(Shaw 1975). Infected Miscanthus sinensis leaves have white
to yellowish white spots that eventually turn brown and are
shredded (Ito & Tokunaga 1935, Waterhouse 1964). Pupipat
(1975) considered the disease only a minor economic problem
on sugarcane.
Miyake discovered this pathogen and made a report of it
in the same publicaon in which Peronosclerospora sacchari
is described (Miyake 1912). Although Miyake included a short
discussion of the disease and briey summarized the oospore
morphology in that publicaon, he did not name the species
at that me and no illustraons were included. In the 1914
English translaon version of Miyake 1912, a note from Miyake
was added (dated July 1913), stang that the pathogen would
be described as a new species under the name of Scelerospora
[sic] miscanthus, T. Miy. In 1926, Troer validated the species,
referring to Miyake 1912 for the descripon. Chu (1953)
provided the rst illustraons of the pathogen and a descripon
of both the sexual and asexual morphology; Chu’s descripon
is consistent with the oospore morphology detailed in Miyake’s
text (1914). Therefore, the descripon provided above is
primarily drawn from Chu (1953).
Further research is needed to address quesons about whether
or not Peronosclerospora miscanthi and Peronosclerospora
sacchari are conspecic. Both species share similar oospore
morphology (Chu 1935, Ito & Tokunaga 1935, Miyake 1914, Telle et
al. 2011). Molecular phylogenec analysis showed that a specimen
of Peronosclerospora miscanthi and a Peronosclerospora sacchari
voucher specimen (BRIP 44241) together a formed a disnct,
highly supported clade (Telle et al. 2011), with the two species
diering by just 0.92 % across two markers (1 426 nt).
The original descripon and validang publicaon for the
species did not designate a holotype; BPI holdings include BPI
187301 dated 1915 from Miscanthus sinensis in Taiwan; this
specimen is here designated as the species neotype.
Peronosclerospora noblei (W. Weston) C. G. Shaw, Mycologia
72: 426. 1980.
Basionym: Sclerospora noblei W. Weston, Phytopathol. 19: 1112.
1929.
Typus: Australia, New South Wales, Glenn Innes, Sorghum leiocladum
(Panicoideae, Andropogoneae) Feb. 1928, R. J. Noble [lectotype
designated here DAR 1075 (MBT 10002151); isotypes BPI 187306, DAR
1076, FH 965379 (MBT 10002152)]. Supplementary Fig. S5 shows the
lectotype BPI 187306.
Descripon: Oogonium ovoid, ellipsoid, pyriform, or subspherical,
28–44 μm. Oogonial wall of variable thickness, typically 5–10
μm but ranging from 3–20 μm giving the appearance of bluntly
rounded projecons and somemes the overall oogonia shape
as gibbous and unsymmetrical; wall color dark, ranging from
golden to rich brown; oogonial stalk fragments oen retained.
Oospores spherical, hyaline to pale golden, 23–28.9 (mode 25–
26.9, range 20–34) μm in diam; wall 1–1.5 μm thick, contents
comprising nely granular material with denser aggregaons
and oil drops, central to eccentric in posion. Germinaon not
observed (Weston 1929; Fig. 4E).
Diagnosis: In describing the species, Weston indicated that
Peronosclerospora noblei is readily disnguishable from
Sclerospora graminicola by the small size of the oospores, their
thin walls, and the uniquely rounded exterior of the oogonium
(versus aened) with rounded surface prominences occurring
due to the variable wall thickness and not due to out-bulgings.
Reference sequence data: Ex-isotype BPI 187306 nucleode
sequences, OK185343 (cox2), OK255496 (28S rDNA).

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Graminicolous downy mildew pathogens
Editor-in-Chief
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E-mail:p.crous@westerdijkinstitute.nl
63
Host range: Sorghum leiocladum, Sorghum plumosum
(Panicoideae, Andropogoneae).
Notes: Peronosclerospora noblei is only known from Australia
(Weston 1929, 1942, Ryley & Langdon 2001, Thines et al.
2008, Farr & Rossman 2021). The type host, the wild sorghum
Sorghum leidocladum, is indigenous to the northern tropical
regions of Australia and not known from elsewhere in the world.
Sorghum leiocladum infected by Peronosclerospora noblei show
malformaon, llers mostly vegetave rather than owering, and
chloroc, frayed leaves held in an abnormal bunch-like manner;
infected leaves eventually become necroc and die (Ryley 2001,
2002, Ryley & Langdon 2001). A second nave Australian grass,
Sorghum plumosum (as Andropogon australis or Andropogon
sp.), is also listed as a host in checklists (Waterhouse 1964, Farr &
Rossman 2021). However, the associaon of Peronosclerospora
noblei with Sorghum plumosum bears further invesgaon,
as molecular phylogenec identy of a Peronosclerospora sp.
specimen on Sorghum plumosum suggests that this organism is
not conspecic with any known Peronosclerospora species and
is not closely aligned with Peronosclerospora noblei (Thines et
al. 2008).
As part of the descripon for Sclerospora noblei, Weston
provided detailed collecon data, but did not specify a
holotype. Examinaon of Weston’s collecons at BPI, DAR,
and FH idened specimens of Sclerospora noblei on Sorghum
leiocladum with the outer envelopes both bearing the label
of the Herbarium of W. H. Weston (BPI 187306, FH 965379).
These specimens were annotated with the same collecon
data that was detailed in the protolog, wrien in Weston’s
hand. There can be no doubt that these are the original
specimens described by Weston; DAR 1075 is therefore used
to lectotypify the species.
Peronosclerospora panici R.G. Shivas et al., Mycol. Progr. 21:
306. 2022.
Typus: Australia, New South Wales, Narromine, on leaves of Panicum
laevinode (as Panicum whitei) (Panicoideae, Andropogoneae), 4 Mar.
1980, G. Stovold (holotype DAR 35733).
Descripon: Conidia globose to sub-globose, rarely ovoid,
hyaline, aseptate, (15–)15–17(–20) × (12–)13–16(–18) μm, thin
walled without operculum or pore (Fig. 5B), germinaon by
germ tube. Sexual morph not observed (Ryley et al. 2022)
Diagnosis: Diers from the sister taxon Peronosclerospora
erichloae based on the nucleode sequence of cox2 (98 %
sequence smiliarity with BRIP 22711).
Reference sequence data: Ex-holotype nucleode sequence
HQ261814 (cox2), HQ261787 (28S rDNA).
Host range: Known only from the type specimen on Panicum
laevinode.
Notes: The host of Peronosclerospora panici, Panicum laevinode,
is a forage species primarily restricted to Australia. Addional
downy mildews have been reported from Panicum species
globally (Peronosclerospora sorghi, Sclerophthora macrospora,
Sclerospora gramincola).
Peronosclerospora philippinensis (W. Weston) C. G. Shaw,
Mycologia 70: 596. 1978.
Basionym: Sclerospora philippinensis W. Weston, J. Agric. Res.,
Washington 19: 118. 1920.
Synonym: ‘Sclerospora maydis’ Reinking, Philipp. J. Sci, A 13: 1.
1918. [nom. illegit., Art. 53.1]
Possible synonym: Sclerospora indica E. J. Butler, Fungi of India
(Calcua): 7. 1931.
Typus: Philippines, Laguna Province, Los Banos, Zea mays, 9 Feb. 1919,
W.H. Weston [lectotype designated here BPI 187314 (MBT10002153);
isotypes BPI 187044, BPI 187311, BPI 187313, FH 965382, FH 965383
(MBT10002154)]. Supplementary Fig. S6 shows the lectotype BPI 18731;
Supplementary Figs S7–S9 show isotypes BPI 187044, BPI 187311, and
BPI 187313, respecvely.
Descripon: Hyphae intercellular throughout host (excluding
root); branched, typically 8 μm diam, irregularly constricted
and inated; simple vesiculiform to subdigitate haustoria, 2 μm
diam. Conidiophores evanescent, nocturnal, erect, 150–400 ×
15–26 μm with basal cell, dichotomously branched two to four
mes; sterigmata conoid to subulate and slightly curved, 10 μm
long. Conidia elongate ellipsoid, elongate ovoid, or rounded
cylindrical, apex slightly rounded, hyaline, usually 17–21 ×
17–39 μm with a minute apiculus at the base, episporium thin,
contents minutely granular, germinang directly by a germ tube.
Oogonia 22.9 μm diam, wall smooth, fragments of oogonial
stalk or antheridia oen adherent (Weston 1920). Oospores
spherical, (15.3–)19.2(–22.6) μm diam, hyaline or straw-colored;
wall smooth, 2.0–3.9 μm thick; contents nely granular with oil
droplets, posioned central to eccentric; germinaon via single
germ tube (Acedo & Exconde 1967; Fig. 5C).
Diagnosis: Eorts to discriminate Peronosclerospora
philippinensis from related taxa with overlapping host ranges
may not provide clear cut dierenaon. Peronosclerospora
philippinensis oospores are reported as smaller in size than
those of Peronosclerospora miscanthi, Peronosclerospora
sacchari, and Peronosclerospora spontanea (Sivanesan & Waller
(1986). Conidial morphology disnguishes Peronosclerospora
philippinensis from Peronosclerospora spontanea, which
has more elongated and slender conidiophores and conidia
(Waterhouse 1964), and from Peronosclerospora sorghi, which
has conidiophores with a basal plug and smaller conidia (Weston
& Uppal 1932, Janruang & Unartngam 2018), but these structures
may be subject to variaon depending on environmental
condions and host (Exconde et al. 1968, Leu 1973, Widianni
et al. 2015). Several authors have quesoned whether or
not Peronosclerospora philippinensis and Peronosclerospora
sacchari are the same species based on morphological similarity,
shared host range, and phenotypic proles generated from
isozyme analyses (Weston 1920, Bonde et al. 1984, Micales et
al. 1988), but at present no conclusive data are available.
At the me of wring (February 2022), NCBI GenBank
contained accessions for 26 sequences idened as
Peronosclerospora philippinensis, but except for the sequences
generated for this paper from the isotype BPI 187044, none
of the sequences are associated with voucher specimens or
type material. Twenty-four of the NCBI accessions are internal
transcribed spacer (ITS) sequences. We recommend exercising
cauon in using these ITS accessions for idencaon, as
the sequences are very diverse and share only 92.9–96.2 %

© 2022 Westerdijk Fungal Biodiversity Instute
Crouch et al.
Editor-in-Chief
Prof. dr P.W. Crous,Westerdijk Fungal BiodiversityInstitute, P.O. Box 85167, 3508 AD Utrecht, The Netherlands.
E-mail:p.crous@westerdijkinstitute.nl
64
identy with one another, suggesng that either some
are misidened or that there are misassemblies of the
sequences resulng from long stretches of repeat elements
known to occur in some downy mildew genera (Thines et al.
2007). Readers are also cauoned that cox2 and rDNA 28S
sequences have limited ulity for idencaon of this species
because these marker sequences share 99.2–100 % identy to
sequence data from voucher materials of Peronosclerospora
miscanthi and Peronosclerospora sacchari. DNA sequencing
from type materials at addional loci may help resolve species
boundaries and provide badly needed diagnosc resources for
Peronosclerospora philippinensis.
Reference sequence data: Ex-isotype BPI 187044 nucleode
sequences OK185341 (cox2), OK181682 (28S rDNA).
Host range: Miscanthus japonicus, Saccharum ocinarum,
Saccharum spontaneum, Sorghum arundinaceum, Sorghum
bicolor, Sorghum halepense, Sorghum propinquum, Zea mays,
Zea mexicana, Zea mexicana × Zea mays hybrids (Panicoideae,
Andropogoneae).
Experimental host range: Peronosclerospora philippinensis
is capable of parasizing several addional hosts under
experimental condions: Andropogon spp., Botriochloa spp.,
Eulalia fulva, Miscanthus japonicus, Sorghum plumosum,
Tripsacum spp., Zea diploperennis, Zea luxurians, and Zea
perennis (Bonde & Peterson 1983). Some of these plants are
common perennial forage and wild prairie grasses in the USA
and globally; therefore, they serve as inoculum reservoirs
(Bonde & Peterson 1983).
Notes: Peronosclerospora philippinensis, causing Philippine
downy mildew, is one of the most destrucve and virulent
pathogens infecng maize, with crop losses reaching as much
as 80–95 % under favorable condions (Exconde & Raymundo
1974, Exconde 1975, CABI 2021). Sugarcane crop losses are
lower, ranging from 9–38 % (CABI 2021). The pathogen is
recognized globally as a threat to plant health, with measures
enacted in several parts of the world to restrict its movement.
According to the European and Mediterranean Plant Protecon
Organizaon Global databases (EPPO 2021), Peronosclerospora
philippinensis is a quaranne pest in Mexico and Morocco and
is subjected to regulaon in China and three EPPO regions due
to its inclusion on the EPPO A1 invasive pest list. In the USA,
Peronosclerospora philippinensis is included in the USDA Plant
Protecon and Quaranne Select Agents and Toxins list (www.
selectagents.gov/sat/list.htm).
Symptoms of Peronosclerospora philippinensis infecng
maize and sorghum are very similar to those of other downy
mildews aecng Poaceae, including chloroc streaks along
the length of the leaf, tassel malformaon, and seed sterility,
which make diagnosis based on symptomology on this host
dicult (Baer & Lalusin 2013, Smith & Renfro 2016). Sugarcane
plants infected with Peronosclerospora philippinensis show
discoloraons at the base of the young leaves, chloroc spots
that turn brick red as leaves age, and thinner canes (Thompson
et al. 2013). These symptoms are very similar to those caused by
Peronosclerospora sacchari and Peronosclerospora spontanea
infecng Saccharum but dier from those of Peronosclerospora
miscanthi, which always causes leaf-spling (Sivanesan &
Waller 1986, Thompson et al. 2013).
The geographic distribuon of Peronosclerospora philippin-
ensis as reported in online resources (such as CABI, EPPO, and
the BPI databases) at the me of wring were conicted. Given
the challenges associated with diagnosing the species using
morphology and symptomology, readers are cauoned that in the
absence of molecular data, the pathogen is easily misdiagnosed
and some reports may be erroneous. Records indicate that
Peronosclerospora philippinensis has been found in Bangladesh,
the Democrac Republic of the Congo, India, Indonesia, Nepal,
Pakistan, and the Philippines (Weston 1920, Doidge 1950, Gaani
1950, Ali 1959, Watson 1971, Bains & Jhooty 1982, Bonde et al.
1984, Farr & Rossman 2021; Faruq et al. 2014, Subedi 2015, Muis
et al. 2016, Ekawa & Gusnawaty 2018, Pakki et al. 2019). Records
of Peronosclerospora philippinensis in Japan and South Africa are
not considered valid by CABI (CABI 2021). Janruang & Unartngam
(2018) have recently suggested that Peronosclerospora
philippinensis should be removed from the list of maize pathogens
present in Thailand. Reports of the pathogen in the USA by EPPO
(2021) and CABI are of uncertain origin but may be based on the
existence of a specimen of Peronosclerospora philippinensis on
maize held by herbarium WSP that is annotated as originang
from Frederick, Maryland, USA (WSP60943). However, WSP60943
was taken from an experimental plant maintained within the
USDA-ARS biosafety level 3 containment facilies on the Fort
Detrick USA Army base. The Peronosclerospora philippinensis
strain used to inoculate the WSP60943 specimen was originally
collected by Ofelio R. Exconde from University of Philippines,
Los Banos College, Laguna, Philippines in 1975 (M. Bonde, G.
Peterson, pers. comm.).
Weston did not specify a holotype, but examinaon of
his specimens at BPI and FH idened several specimens
of Sclerospora philippinensis on Zea mays with the outer
envelopes bearing the label of the Herbarium of W. H. Weston
and annotated with the same collecon data that was detailed
in Weston’s protolog. Labels for BPI 187314, BPI 187044 and FH
965383 are wrien in Weston’s hand, and the two BPI specimens
contain Weston’s handwrien annotaons together with his
correspondence regarding the material (BPI 187314). There can
be no doubt that these are the original specimens described by
Weston; BPI 187306 is therefore used here to lectotypify the
species.
Peronosclerospora sacchari (T. Miyake) Shirai & Hara, List of
Japanese fungi hitherto unknown, 3rd edn: 257. 1927.
Basionym: Sclerospora sacchari T. Miyake, Rep. Sugar Exper. Stn,
Gov. Formosa 1: 12. 1912.
Synonyms: Sclerospora sorghi-vulgaris Mundk. [as (Kulk.)
Mundk.], Indian J. Agric. Sci. 20: 138. [1950] 1951.
‘Peronosclerospora sacchari’ (T. Miyake) C.G. Shaw, Mycologia
70: 595. 1978. [nom. illegit., Art. 53.1]
Typus: Taiwan, Saccharum ocinarium (Panicoideae, Andropogoneae)
8 Oct. 1910, collector not specied [lectotype designated here BPI
187331 (MBT 10002155)]. Supplementary Fig. S10 shows the lectotype
BPI 187331.
Descripon: Conidiophores fugacious, erect, hyaline, 160–170
μm long; wall smooth, thin; base slightly narrower (10–15 μm
broad), one or rarely two septate; middle part about two to
three mes broader than the base apex; two or three mes
branched two or three mes each branch stocky and conical
shaped. Conidia ellipcal or oblong, hyaline, 25–41 × 15–23

© 2022 Westerdijk Fungal Biodiversity Instute
Graminicolous downy mildew pathogens
Editor-in-Chief
Prof. dr P.W. Crous,Westerdijk Fungal BiodiversityInstitute, P.O. Box 85167, 3508 AD Utrecht, The Netherlands.
E-mail:p.crous@westerdijkinstitute.nl
65
μm, or 49–54 × 19–23 μm, apex rounded, base slightly apiculate
or rounded, wall thin and smooth; direct germinaon by germ
tubes. Oogonium irregularly ellipcal, castanian brown, 49–58
× 55–73 μm; wall thickness unequal. Oospores globular, yellow,
40–50 μm diam, wall 3.8–5 μm thick; germinaon by germ tubes
(Miyake 1912; Fig. 5D).
Diagnosis: Peronosclerospora sacchari shares similar
morphology, host range, and induces similar symptoms in the
parasized host as Peronosclerospora philippinensis (Miyake
1912, Weston 1920, Ito & Tokunaga 1935, Chu 1953, Telle et
al. 2011). Elazegui & Exconde (1968) reported size and shape
dierences from the conidiophores of Peronosclerospora
sacchari and Peronosclerospora philippinensis, but these
dierences might be the result of interspecic variability and/
or environmental inuences (Leu 1973, Widianni et al. 2015).
Refer to Diagnosis secon for Peronosclerospora philippinensis
above for addional discussion.
Reference sequence data: Ex-BRIP 44241A nucleode sequences
EU116052 (cox2), HQ261764 (28S rDNA).
Host range: Saccharum edule, Saccharum ocinarum,
Saccharum robustum, Saccharum spontanea, Tripsacum
dactyloides, Sorghum vulgare var. technicum, Zea mays, and
Zea mexicana (Panicoideae, Andropogoneae).
Experimental host range: Bonde & Peterson (1981, 1983)
showed that under experimental condions, Peronosclerospora
sacchari systemically infects 18 species of grasses in the genera
of Andropogon, Bothriochloa, Eulalia, Schizachyrium, and
Sorghum (Bonde & Peterson 1981), suggesng a possible role
for these plants as alternate hosts.
Notes: Peronosclerospora sacchari causes sugarcane downy
mildew on sugarcane or maize ( also known as leaf stripe disease).
This species is known from the Western-Pacic region of Asia and
Oceania (Farr & Rossman 2021) where it has signicant economic
impact on the sugarcane industry (Sugarcane Research Australia
2019). The most characterisc symptoms of Peronosclerospora
sacchari on sugarcane are chloroc leaf stripes that turn red
with age, brown lesions on external stalk surfaces, and stunng
of infected stools.
The rst sighng of Peronosclerospora sacchari causing a leaf
spling disease occurred in 1909 at the Sugar Experiment Staon
in Taiwan on sugarcane elds planted with canes of Australian
origin (Miyake 1912). By 1912, the disease was so widespread
and destrucve that the Taiwanese government ordered
destrucon of all aected sugarcane cungs across two cies
and 18 villages (Miyake 1912). Severe epidemics on sugarcane
occurred in Taiwan between 1962–1967 (Payak 1967). In India,
Peronosclerospora sacchari was rst recovered from maize from
the Tarai area of Uar Pradesh (where sugarcane was planted
widely) in 1968 (Singh 1968). Since then, Peronosclerospora
sacchari outbreaks on maize have been sporadic and natural
infecon of sugarcane has not been observed in India (Payak
1975a, b, Sugarcane Research Australia 2019). In the late 1950s
the pathogen was introduced to Australia through infected
sugarcane cungs, producing severe economic losses (Pupipat
1975, Suma & Magarey 2000), but an aggressive eradicaon
plan enacted by the government resulted in the eradicaon
of Peronosclerospora sacchari from Australia by the mid-
1960s (Suma & Magarey 2000, Shivas et al. 2012). Reports
of Peronosclerospora sacchari from the Eastern hemisphere
(Central America, South America and the USA) are unconrmed
as these reports are derived from checklist publicaons (Farr &
Rossman 2021).
A holotype was not designated when the species was
described, but the collecon details for BPI 187331 match
those described by Miyake (Miyake 1912); we therefore use this
specimen to lectotypify Peronosclerospora sacchari.
Peronosclerospora sargae R.G. Shivas et al., Australas. Pl.
Pathol. 41: 128. 2012.
Typus: Australia, Northern Territory, Florence Falls, Sorghum morense,
(Panicoideae, Andropogoneae), 13 Mar. 2000, R.G. Shivas, I.T. Riley, C. &
K. Vánky (holotype BRIP 27691).
Descripon: Oogonia globose, subglobose to broadly ellipsoidal,
occasionally irregularly polyangular, pale yellow to yellowish
brown, (30–)37.9(–47) μm diam; wall 2–8 μm thick, smooth,
uneven. Oospores globose, pale yellow, (24–)29.3(–34) μm
diam, oen containing large vacuole; wall (1.5–)2.1(–3.0) μm
thick, even, smooth. Asexual morph not observed (Shivas et al.
2012; Fig. 6C).
Diagnosis: Peronosclerospora sargae shows similar
morphological features to Peronosclerospora noblei; however,
these species can by disnguished based on the thickness of
the oospore wall, host range, and sequence of the cox2 and 28S
rDNA loci (Shivas et al. 2012).
Reference sequence data: Ex-holotype nucleode sequences
HQ261809 (cox2) and HQ261782 (28S rDNA).
Notes: Peronosclerospora sargae has not been reported since its
inial descripon (Farr & Rossman 2021) and is only known from
the type specimen (Telle et al. 2011, Shivas et al. 2012). The host,
Sorghum morense (Down’s sorghum), is endemic to tropical
regions of Australia and several islands north of Australia; the
impact of Peronosclerospora sargae on populaons of this wild
grass is unknown.
Peronosclerospora schizachyrii R.G. Shivas et al., Mycol. Progr.
21: 306. 2022.
Typus: Australia, Queensland, Mareeba Wetlands, Schizachyrium fragile
(Panicoideae, Andropogoneae), 27 Apr. 2018, J. Kruse, M.J. Ryley, S.M.
Thompson, M.D.E. & R.G. Shivas (holotype BRIP 67070).
Descripon: Oogonia globose to sub-globose, golden brown,
(35–)41–55(–65) μm diam; wall 6–32 μm thick, uneven,
polyangular, smooth. Oospores globose to sub-globose, hyaline,
(26–)29–39(–47) μm in diam, adnate with oogonial wall, with a
single vacuole; wall 1–4 μm thick, even, smooth. Asexual morph
not observed. (Ryley et al. 2022; Fig. 6A).
Diagnosis: Diers from the sister taxon Peronosclerospora
erichloae on the basis of the nucleode sequence of cox2 (98 %
sequence smiliarity with BRIP 22711).
Reference sequence data: Ex-holotype nucleode sequences
OK336452 (cox2) and OK350689 (28S rDNA).

© 2022 Westerdijk Fungal Biodiversity Instute
Crouch et al.
Editor-in-Chief
Prof. dr P.W. Crous,Westerdijk Fungal BiodiversityInstitute, P.O. Box 85167, 3508 AD Utrecht, The Netherlands.
E-mail:p.crous@westerdijkinstitute.nl
66
Host range: Known only from the type specimen on Schizachyrium
fragile.
Notes: Peronosclerospora schizachyrii is the only known downy
mildew from naturally infected hosts in the genus Schizachyrium,
although experimental infecon of Schizachyrium spp. by isolates
idened as Peronosclerospora sacchari and Peronosclerospora
philippinensis has been demonstrated (Bonde & Peterson 1983).
Infecon by Peronosclerospora schizachyrii results in spling of the
leaf blade into tangled vascular strands that can measure up to 10
cm long. The host, Schizachyrium fragile, is endemic to northern
and central regions of Australia; the impact of Peronosclerospora
schizachyrii on populaons of this wild grass is unknown.
Peronosclerospora sehimas M.J. Ryley et al., Mycol. Progr. 21:
307. 2022.
Typus: Australia, Northern Territory, Arnhem Highway, Jabiru, Sehima
nervosum, (Panicoideae, Andropogoneae), 12 Apr. 2006, M.J. Ryley &
R.G. Shivas (holotype BRIP 49806).
Descripon: Oogonia globose to sub-globose, light golden
brown, (38–)45–58(–63) μm diam; wall 3–15 μm thick, smooth,
uneven. Oospores one per oogonium, globose, (28–)34–42(–46)
μm diam, adnate with oogonial wall, with a single vacuole;
wall 2–4 μm thick, hyaline, even, smooth. Asexual morph not
observed (Ryley et al. 2022; Fig. 6B).
Diagnosis: Diers from the related taxa Peronosclerospora
ischaemi and Peronosclerospora jamesiae based on the
nucleode sequence of cox2 (98 % sequence smiliarity); diers
from other Peronosporaceae based on its parasism of Sehima
nervosum.
Fig. 6. A. Peronosclerospora schizachyrii, oospores. B. Peronosclerospora sehimas, oospores. C. Peronosclerospora sargae, oospores. D. Peronosclerospora
sorghi, sporangiophores at two stages (young and mature) and oospores. Arrows point to germinang oospores and sporangia. Illustraons were
prepared from published reference images in Weston (1932), Shivas (2012), Ryley et al. (2021) and Ryley et al. (2022).

© 2022 Westerdijk Fungal Biodiversity Instute
Graminicolous downy mildew pathogens
Editor-in-Chief
Prof. dr P.W. Crous,Westerdijk Fungal BiodiversityInstitute, P.O. Box 85167, 3508 AD Utrecht, The Netherlands.
E-mail:p.crous@westerdijkinstitute.nl
67
Reference sequence data: Ex-holotype nucleode sequence
OK336453 (cox2).
Host range: Known only from the type specimen on Sehima
nervosum.
Notes: The host is widespread in Australia, tropical parts of Asia,
and Africa, however Peronosclerospora sehimas is the only
known downy mildew from hosts in the genus Sehima. Infecon
by Peronosclerospora sehimas results in spling of the leaf blade
into tangled vascular strands that can measure up to 10 cm long.
Peronosclerospora sorghi (W. Weston & Uppal) C.G. Shaw,
Mycologia 70: 596. 1978.
Basionym: Sclerospora graminicola var. andropogonis-sorghi
Kulk., Memoirs of the Dept. Agric. India, Bot. Ser. 55: 272. 1913.
Synonyms: Sclerospora sorghi (Kulk) W. Weston & Uppal,
Phytopathol. 22: 582. 1932.
Sclerospora sorghi W. Weston & Uppal, Phytopathol. 22: 582.
1932.
Sclerospora andropogonis-sorghi (Kulk.) Mundk., Indian J. Agric.
Sci. 20: 138. 1951.
‘Sclerospora andropogonis-sorghi’ (Kulk.) Kulk. ex Safeeulla &
Thirum. Mycologia 47: 177. 1955. [nom. nud., Art. 11.2]
Sorosporium andropogonis-sorghi S. Ito, Trans. Sapporo Nat.
Hist. Soc. 14: 93. 1935.
Typus: India, Coimbatore, Sorghum bicolor (Panicoideae,
Andropogoneae), collector not specied [lectotype designated here BPI
187336 (MBT 10002156)]. Supplementary Fig. S11 shows the lectotype
BPI 187336.
Descripon: Conidiophores erect, spreading, comprising basal
cell, main axis more or less complex, usually dichotomously
branched, expanded top; 100–150 μm length to the septum
(rarely by a paral, ring-like thickening); main axis 15–25 μm
diam; basal cell 7–9 μm wide, knobbed or bulbous at base.
Branching comprising short, stout dichotomies usually with
primary, secondary, and terary branches terminang in tapering
sterigmata; sterigmata 13 μm long. Conidia suborbicular, hyaline,
21–24.9 × 19–22.9 μm (range 15–28.9 × 15–26.9 μm) diam, thin
walled, germinaon direct by germ tubes. Oogonia with thick,
irregularly polygonally-angled oogonial wall closely enveloping
the oospore. Oospores spherical, hyaline, 31–36.9 μm (mode
35–36.9 μm, range 25–42.9 μm) diam; wall light Mars Yellow,
1.1–2.7 (range 0.3–4.3 μm) thick; contents nely granular with
oil globules, posioned centrally or eccentric; germinaon direct
by a branched, hyaline germ tube, 4.4 μm average width (range
2.5–8.3 μm) (Weston & Uppal 1932; Fig. 6D).
Diagnosis: Direct germinaon of conidia readily disnguishes
Peronosclerospora sorghi from Sclerospora graminicola and
other Peronosporaceae parasites of grasses with sporangia that
germinate by means of zoospores. Disnguished from other
Peronosclerospora species by molecular analyses including
phylogenec analysis of the cox2 marker, isozyme phenotypes,
and SSR fragment analysis (Bonde et al. 1984, Micales et al.
1988, Thines et al. 2008).
Reference sequence data: Ex-HUH 897 (also referred to as
“2ps001”) nucleode sequences EU116055 and HQ261790
(cox2), HQ261763 (28S rDNA).
Host range: Sorghum bicolor (Andropogon sorghum) Sorghum
spp., Zea mays, Zea mexicana (Panicoideae, Andropogoneae).
Possible reports from Panicum maximum and Roobellia exalta.
Notes: Peronosclerospora sorghi is primarily associated with
destrucve global outbreaks of sorghum and maize downy
mildew diseases. This species provides a textbook example of
an invasive pathogen that moved from its endemic range in
the Old World into the New World, rst invading Central and
South America during the 1950s and later the USA in the 1960s
(Fredericksen & Renfro 1977). The pathogen quickly became
widespread in the Americas aer its introducon, causing heavy
damages to sorghum and maize producon. For example, in
1969 in the USA state of Texas, sorghum and maize losses due
to Peronosclerospora sorghi were esmated at $2.5 million
(Fredericksen et al.1969), the equivalent of $712.6 million in
2021 dollars.
The rst known sighng of Peronosclerospora sorghi
occurred in 1907, when Butler reported the pathogen infecng
jowar (sorghum; Sorghum bicolor) in India (Butler 1907).
Kulkarni provided the rst name for the pathogen in 1913
when he described Sclerospora graminicola var. andropogonis-
sorghi, primarily based on the observaon that the conidia
of the sorghum pathogen germinated by hyphae and not by
zoospores, disnguishing it from Sclerospora graminicola
sensu stricto (Kulkarni 1913). Weston & Uppal (1932) described
Sclerospora sorghi in 1932 on the basis of Sclerospora
graminicola var. andropogonis-sorghi. Given the parenthecal
citaon of Kulkarni and the fact that Weston & Uppal did not
designate a type, their apparent intenon was to make a new
combinaon. But in naming the species, the replaced synonym
did not supply the nal epithet, and as a result some authors
have treated Sclerospora sorghi as a replacement name (Shaw
1978) rather than a combinaon. However, the provisions of
Art. 24.4 apply in this situaon, allowing for the designaon of
a binary combinaon instead of an infraspecic epithet without
change of authorship. Consequently, Sclerospora sorghi (Kulk.)
W. Weston & Uppal was published as a new combinaon at a
new rank (comb. & stat. nov.).
A holotype has not been designated for this species. BPI
187336 is part of the collecon reported by Kulkarni (1913),
and the specimen contains abundant, well preserved material,
including both the conidial and oospore stages. We therefore
designate BPI 187336 as the lectotype for Peronosclerospora
sorghi.
Peronosclerospora spontanea (W. Weston) C.G. Shaw,
Mycologia 70: 597. 1978.
Basionym: Sclerospora spontanea W. Weston, J. Agric. Res,
Washington 20: 678. 1921.
Typus: Philippines, Laguna Province, Los Banos, Luzon, on leaves and
shoots of Saccharum spontaneum (Panicoideae, Andropogoneae), 17
Aug. 1921, W.H. Weston [lectotype designated here BPI 187043 (MBT
10002157); isotype BPI 187073 (MBT 10002158)]. Supplementary Fig.
S12 shows the lectotype BPI 187043; Supplementary Fig. S13 shows
isotype BPI 187073.
Descripon: Conidiophores evanescent, nocturnal, erect, single
or grouped, 350–550 μm length, basal cell 140–260 × 5–8 μm
and usually exceeding or at least equaling in length the extent
of the main axis from the septum to the primary branches;

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68
more or less complex dichotomous branching system, and
straight terminal sterigmata 13 μm long. Conidia elongately
ellipsoid or cylindrical, hyaline, mostly 39–45 × 15–17 μm diam,
nely granular content, thin wall, rounded apex lacking papilla,
rounded base with apiculum of aachment, germinaon by
germ tubes. Oogonia not observed (Weston 1921; Fig. 7A).
Diagnosis: Sclerospora spontanea is disnguished from
Peronosclerospora philippinensis on maize hosts by having
conidiophores that are more elongate and slenderer, with
basal cells less knobbed and expanded at the base; branches
longer, slenderer, less constricted at point of origin; sterigmata
longer; slenderer and straighter conidia. However, cauous
interpretaon of asexual characters is recommended, as
variaon due to environmental factors may hinder accurate
species discriminaon.
Reference sequence data: No sequence data available from type
material or bona de specimens.
Host range: Miscanthus japonicus, Saccharum spontaneum,
Saccharum ocinarum, Zea mays, Zea mexicana (Panicoideae,
Andropogoneae).
Experimental host range: Peronosclerospora spontanea
can infect Miscanthus japonicus and Zea mexicana under
experimental condions (Weston 1921).
Notes: Peronosclerospora spontanea is known from the
Philippines where it causes downy mildew disease of Saccharum
spontaneum (bugang grass) and Zea mays (Weston 1921,
Pupipat 1975) and has been documented once from culvated
sugarcane (Saccharum ocinarum; Weston 1921). The pathogen
may be limited to the Philippines, where Weston reported
three sites with heavy natural infecons of wild bugang grass
and one natural infecon of a single stand of sugarcane in the
Visayas region (Weston 1921). However, a possible incidence of
Peronosclerospora spontanea from Thailand during 1938 has
been noted (Pupipat 1975, Shaw 1975, Farr & Rossman 2021).
The type host (Saccharum spontaneum) is a wild sugarcane
nave to India that has been introduced across tropical
regions of Africa, Asia, and the Mediterranean, somemes as
an outcome of its widespread use in sugarcane breeding; it is
oen considered a noxious weed. Saccharum sponteaneum
is not greatly damaged by infecons of Peronosclerospora
spontanea, exhibing only minor chloroc leaf striping and no
deformaon (Weston 1921). In contrast, Peronosclerospora
spontanea is described as extremely debilitang to maize, with
symptoms and damages to maize similar to those produced by
Peronosclerospora philippinesis (Weston 1921).
In his descripon of the species, Weston did not designate
a holotype. Weston’s August 1921 collecons of Saccharum
spontaneum colonized by oogonia of Sclerospora spontanea
are accessioned as BPI 187043 and BPI 187073 and match
the published collecon details; BPI 187043 is hereby used
to lectotypify Peronosclerospora spontanea. One addional
specimen of Sclerospora spontanea collected in December 1921,
BPI 187342, consists of dried conidia scraped from the surface
of diseased maize leaves that had been inoculated from conidia
originally harvested from Saccharum spontaneum, and includes
a typewrien note signed by Weston (Supplementary Fig. S14).
Peronosclerospora westonii J.A. Crouch & Thines sp. nov.
MycoBank MB 840574.
Synonyms: ‘Sclerospora westonii’ Sriniv. et al., Bull. Torrey Bot.
Club 88: 94. 1961. [nom. inval., Art. 40.1]
‘Peronosclerospora westonii’ (Sriniv. et al.) C.G. Shaw, Mycologia
70: 597. 1978. [nom. inval. Art. 35.1]
Typus: Illustraon in Bull. Torrey Bot. Club 88: 93, g. 7, 1961 (holotype
designated here) based on collecon made in India, Poona, Iseilema
prostratum (as Iseilema laxum; Panicoideae, Andropogoneae), Jul./Aug.
1960, M.C. Srinivasan, M.J. Narasimhan, M.J. Thirumalachar.
Descripon: Conidiophores 600–1 000 μm long, with single basal
compartment; 9–11.5 μm broad at the basal compartment, 20–
27 μm broad at main axis branching. Dichotomous branching,
20–25 μm high × 12–15 μm spread; typically limited to 2–4
primary branches with 2–3 obconical tapering sterigmata with
conidia; rarely main axis producing secondary branches. Conidia
globose to ovoid, hyaline 12–19 μm in diam, thin-walled, with
granular contents at maturity, germinang by germ tubes.
Oogonia spherical, subglobose, 40–50 μm diam, with granular
contents. Oospores spherical, golden-brown, 23–29 μm diam,
wall 6–9 μm thick, covered by the outer oogonial wall layer.
(Srinivasan et al. 1961; Fig. 7B).
Diagnosis: In common with Peronosclerospora dichanthiicola,
Peronosclerospora westonii has an aggregated, undierenated
conidiophore branch structure, a feature that disnguishes
the species from the well-developed branching structure of
Peronosclerospora noblei, Peronosclerospora philippinensis,
Peronosclerospora sorghi, and Peronosclerospora spontanea.
However, conidia of Peronosclerospora westonii are smaller
than those of Peronosclerospora dichanthiicola, measuring
12–19 μm diam versus 21–28 × 15–18 μm, respecvely.
Peronosclerospora westonii occurs on the same host species
as Peronosclerospora iseilemas, but can be dierenated by
dierences in oospore size, with the spherical golden-brown
oospores of Peronosclerospora westonii measuring 23–29
μm diam with thick endosporium walls of 6–9 μm thickness
vs. the spherical, pale oospores of Sclerospora iseilemas
measuring 38–50 μm diam with endosporium walls of 3.0–3.5
μm thickness.
Reference sequence data: No sequence data available from type
material or bona de specimens.
Notes: To our knowledge, Peronosclerospora westonii has not
been reported since the species was rst diagnosed in 1961
(Srinivasan et al. 1961, Waterhouse 1964, Farr & Rossman
2021). The type host Iseilema prostratum (musal grass) is a
common forage grass distributed in the waterlogged tropical
regions of southern India and connental southeast Asia. The
original report of P. westonii described leaves with chloroc
yellow streaking that became necroc and eventually led to leaf
shredding (Srinivasan et al. 1961).
Sclerospora westonii Sriniv. et al. is an invalid name, as
Srinivasan et al. (1961) neglected to designate a type (Art. 40.1,
Turland et al. 2018). The invalid status of Sclerospora westonii
also renders P. westonii (Sriniv. et al.) C.G. Shaw invalid, as the
name is based on an invalid basionym (Art. 35.1, Turland et al.
2018). It is unknown whether specimens ulized by Srinivasan
et al. (1961) were formally lodged in a reference collecon;

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69
therefore, an illustraon is ulized here as the holotype for
the species, providing clear morphological features including
conidiophores, sterigmata, conidia, oogonium, and oospores
(Srinivasan et al. 1961).
‘Peronosclerospora zeae’ C. L. Yao, Curr. Genet. 22: 415–420.
1992. [nom. inval., Art. 30.9, 36.1., 40.1]
Typus: Non designatus.
Notes: The rst appearance of this name is found in Yao’s (1991)
dissertaon; however, there was no descripon and a type
was not designated. Yao et al. (1992) later applied this name
and inaccurately referenced the dissertaon as the eecve
publicaon. Later authors considered the strains used by Yao
(1991) to be Peronosclerospora maydis (Perumal et al. 2008).
Poakatesthia Thines & Göker, Mycol. Res. 111(12): 1381. 2007.
Type species: Poakatesthia pennise (R.G. Kenneth & J. Kranz)
Thines & Göker, Mycol. Res. 111: 1381. 2007.
Notes: The genus Poakatesthia was designated to accommodate
the pathogen originally described as Plasmopara pennise
based on the producon of sporangiophores that are shaped
similarly to those found in the genus Plasmopara (Kenneth &
Kranz 1973). Thines & Göker (2007) designated the new genus
Poakatesthia based on the unique morphology of the haustoria
Fig. 7. A. Peronosclerospora spontanea, sporangiophore and sporangia (some germinang). B. Peronosclerospora westonii, sporangiophore,
germinang sporangia and oospores. C. Poakatesthia pennise, sporangiophore. Illustraons were prepared from published reference images in
Weston (1921), Srinivasan et al. (1961), Titatarn & Syamanda (1978) and Thines et al. (2007).

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70
and cox2 sequence data that characterizes Poakatesthia
pennise. Poakatesthia contains one species and is known only
from Ethiopia as a parasite of Pennisetum glaucum.
Poakatesthia pennise (R.G. Kenneth & J. Kranz) Thines & Göker,
Mycol. Res. 111: 1381. 2007.
Synonym: Plasmopara pennise R.G. Kenneth & Kranz, Trans.
Brit. Mycol. Soc. 60: 591. 1973.
Typus: Ethiopia, Bako/Shoa, Pennisetum glaucum (Panicoideae,
Paniceae), Oct. 1968, J. Kranz (holotype IMI 137328c).
Descripon: Sporangiophores hyaline, amphigenous, erect,
300–580 μm high; trunk 0.55–0.77 of total height × 8–11 μm
width; dichotomously branched once or twice, then branched
irregularly monopodially to subdichotomously two or three
mes at right angles. Ulmate branchlets straight or slightly
curved, usually two divaricate at apices of nal branch, tapered
with truncate p, 4.7–9.5 μm long × 3.2 μm wide at base; 1–2
ulmate branchlets somemes along sides on nal branch,
4.7–12.6 μm long. Sporangia hyaline, wide obovoid with +/-
aened apical end and poroid papilla, base peducellate;
19–23.7 × 14.2–17 (19) μm. Oogonia not observed (Kenneth &
Kranz 1973; Fig. 7C).
Diagnosis: Sporangiophore morphology similar to Plasmopara
but diers based on obovoidal to egg shaped sporangia with
aened apex, intracellular mycelium and parasism of
Pennisetum pennise. Uniquely diagnosed based on nucleode
sequence of cox2 that shares just 94.5 % identy with Viennoa
oplismeni, its most closely related species.
Reference sequence data: Ex-holotype nucleode sequence
EF426475 (cox2).
Notes: Poakatesthia pennise has not been reported since its
inial descripon on pearl millet (Pennistum glaucum; Kenneth
& Kranz 1973, Thines et al. 2007, 2008, Thines & Choi 2016,
Farr & Rossman 2021), one of the most important staple food
crops in India and several regions of Africa. Disease symptoms
on infected plants were described as minor, and largely aected
lower leaves of plants across an experimental plot in a remote
region of the Ethiopian highlands (Kenneth & Kranz 1973). Inial
symptoms are diuse, small watersoaked spots or stripes that
expand and coalesce to form irregular brown stripes between
the veins leading to eventual necrosis (Kenneth & Kranz 1973).
Since pearl millet was rst introduced by seed to this isolated
region of Ethiopia in 1966, Kenneth & Kranz speculated that the
pathogen might have originated from one of several indigenous
Pennisteum spp. growing in the area (Kenneth & Kranz 1973).
Sclerophthora Thirum., C.G. Shaw & Naras., Bull. Torrey Bot.
Club 80: 304. 1953.
Type species: Sclerophthora macrospora (Sacc.) Thirum. et
al., Bull. Torrey Bot. Club 80: 299. 1953.
Notes: Sclerophthora was erected by Thirumalachar et al. (1953) to
accommodate Sclerophthora macrospora, a species that exhibits
morphological characters typical of both Sclerospora (thick-
walled oospores) and Phytophthora (hyphal sporangiophores,
large, lemon-shaped phytophthora-like sporangia). The genus
diers from all other Peronosporaceae genera, as it typically
produces hardly dierenated sporangiophores, sporangia
that germinate to produce biagellate zoospores, and thick-
walled oospores measuring 30–80 μm diam. It is unknown
whether indirect oospore germinaon is a common trait for
Sclerophthora, as oospore germinaon has not been described
for the other ve species currently assigned in the genus. It
should be noted that the great variaon in symptoms caused
by the dierent species, as well as some morphological traits
of the sporangia produced render it doubul if the genus is
monophylec.
Sclerophthora cryophila W. Jones, Canad. J. Bot. 33: 352. 1955.
Typus: Canada, Brish Columbia, Saanichton, Dactylis glomerata
(Pooideae, Poeae), 1 Jun. 1948, W. Jones [holotype designated here
DAOM 20643 (MBT 10002159)]. Supplementary Fig. S15 shows the
holotype DAOM 20643.
Descripon: Sporangiophores short, sterigma-like, unbranched.
Sporangia obpyriform, hyaline, (22.5–)30.5–38(–45.5) μm ×
(11.5–)15–19(–22.5) μm, apically poroid, pedicels persistent;
nocturnal under natural condions. Oogonia subglobose to
spherical, sinuous, golden to amber-brown, (29.5–)38.5(–
51.5) μm diam; wall 1.9-3.8 μm thick (average 3.7). Antheridia
paragynous. Oospores spherical, (20–)31.8(–37.5) μm diam; wall
(1.5–)2.6(–3.5) μm thick, conuent with oogonial wall (Jones
1955; Fig. 8A).
Diagnosis: Disnct from Sclerophthora macrospora in that it
has smaller oospores, oogonia, and sporangia, and thinner
oogonium walls.
Reference sequence data: No sequence data available from type
material or bona de specimens.
Host range: Dactylis glomerata (Pooideae, Poeae). Possible
hosts: Apluda muca, Dichanthium annulatum, Digitaria
marginata, Heteropogon contortus (Panicoideae).
Notes: Sclerophthora cryophila was rst reported on the
cool-season grass Dactylis glomerata (orchard grass) from
Canada (Jones 1955). Orchard grass infected by Sclerophthora
cryophila in eld plots produced symptoms described as similar
to the eects of frost injury, with yellow/brown streaks on
leaves and occasional pale brown to pale cream discoloraon
of inorescence sheaths (Jones 1955). Although the type host
is widely distributed across North America in stands of wild
grown plants or culvated as a high-quality forage grass, there
have not been reports of Sclerophthora cryophila from orchard
grass since the collecon from the original outbreak (Jones
1955).
There have been reports of Sclerophthora cryophila
from India aecng four hosts in the subfamily Panicoideae
(Srinivasan & Thirumalachar 1962, Safeeulla et al. 1963). The
morphology of the pathogen described from Apluda muca,
Dichanthium annulatum, Digitaria marginata, and Heteropogon
contortus is consistent with Sclerophthora cryophila (Srinivasan
& Thirumalachar 1962). Given the host range associated with
these reports and our current understanding of downy mildew
pathogens as mostly narrowly host-specic organisms (Thines &
Choi 2016), the idencaon of Sclerophthora cryophila from

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Graminicolous downy mildew pathogens
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71
these warm-season grasses suggests that the species may be
a complex of morphologically similar species. This is parally
supported by the results of cross-inoculaon experiments, where
strains of Sclerophthora cryophila from Digitaria marginata and
Heteropogon contortus were unable to infect each other’s hosts
(Srinivasan & Thirumalachar 1962).
Under natural condions, Sclerophthora cryophila
produces sporangiophores nocturnally for just a few hours in
the early morning under conducive condions, but sporangia
collected from warm-season hosts exhibit no periodicity and
can be readily induced by oang infected leaf secons on
water (Srinivasan & Thirumalachar 1962), which is similar
Fig. 8. A. Sclerophthora cryophila, sporangiophores, sporangia with zoospores, and oospores. B. Sclerophthora lolii, sporangiophores, sporangium
with emerging zoospores, and oospores. C. Sclerophthora macrospora, sporangiophores (with sporangia lled with undierenated cytoplasm,
empty, with emerging zoospores, or germinang), and oospores. D. Sclerophthora rayssiae, sporangiophore, sporangium with emerging zoospores,
and oospores. E. Sclerophthora zeae, sporangiophore, sporangium with emerging zoospores, and oospore. Illustraons were prepared from published
reference images in Jones (1955), Srinivasan & Thirumalachar (1962), Kenneth (1963), Waterhouse (1964), Payak & Renfro (1967) and Ryley et al.
(2021).

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72
to Sclerophthora macrospora (Thirumalachar et al. 1953),
Sclerospora graminicola, and Sclerospora sorghi (Safeeulla &
Thirumalachar 1956).
A holotype specimen was not formally designated for
Sclerophthora cryophila. Jones indicated in the protolog that type
materials were deposited in the herbarium of the Plant Pathology
Laboratory, Saanichton, B.C.; the Saanichton collecons were
later transferred to DAOM. DAOM holdings of Sclerophthora
cryophila include six specimens on Dactylis glomerata, but just
one of these specimens (DAOM 20643) was collected on 1 Jun.
1948 by W. Jones, consistent with the species protolog. DAOM
20643 is clearly the sole specimen used to describe Sclerophthora
cryophila and is therefore the holotype (Art. 9.1).
Sclerophthora lolii J.A. Crouch & Thines, sp. nov. MycoBank MB
840575.
Synonym: ‘Sclerophthora lolii’ R.G. Kenneth, Israel J. Bot. 12:
139. 1963. [nom. inval. Art. 40.1].
Typus: Illustraon in Israel J. Bot. 12: 137–138, g. 1–3, 1964 (holotype
designated here) based on collecon made in Israel, Mikve, Lolium
rigidum (Pooideae, Poeae), Feb. 1962, R.G. Kenneth.
Descripon: Sporangiophores hyaline, slender, bearing
sporangia. Sporangia lemon-shaped, 40.7–55.0(–63.7) ×
25.2–35.0 μm; base with persistent peduncle, apex papillate,
poroid, thin-walled; 10–15 pyriform zoospores produced within
sporangium, 7.8–10.7 μm long, escaping through sporangial
apex. Oogonia spherical to subspherical, sinuous, 25.2–28.8 μm
diam. Oospores spherical, golden brown, 10.8–18.0 μm diam,
smooth-walled, moderately thin-walled, centrally located within
conuent thick oogonial walls (Kenneth 1963; Fig. 8B).
Diagnosis: Sporangia size and shape similar to Sclerophthora
cryophila and Sclerophthora raysiae, but Sclerophthora lolii can
be discriminated from these two species based on its smaller
oogonia and oospore size. The length of the pyriform zoospores
(7.8–10.7 μm), as with Eraphthora butleri, Sclerophthora
raysiae, and Sclerophthora zeae, is disncve among the
Peronosporaceae (Kenneth 1963).
Reference sequence data: No sequence data available from type
material or bona de specimens.
Notes: Weedy, immature wild ryegrass (Lolium rigidum) infected
with Sclerophthora lolii exhibit only mild disease symptoms,
appearing as localized yellow patches on leaves that eventually
necroze without inducing leaf shredding (Kenneth 1964). To
our knowledge, there have been no subsequent reports of this
pathogen since the original 1962 discovery in Israel.
Sclerophthora lolii R.G. Kenneth was not validly published
since a type specimen was not designated but was required at
the me of publicaon (Art. 40.1; Turland et al. 2018). Kenneth’s
collecon at HUJ, including his specimen of this species, appears
to have been lost, but published illustraons of the original
material clearly depict the diagnosc features of the organism
and are therefore designated as the holotype for the newly
validated species.
Sclerophthora macrospora (Sacc.) Thirum. et al., Bull. Torrey
Bot. Club 80: 299. 1953.
Basionym: Sclerospora macrospora Sacc., Hedwigia 29: 155.
1890.
Synonyms: Sclerospora kriegeriana Magnus, Verh. Ges. Deutsch.
Naturf. 67: 100. 1896.
Kawakamia macrospora (Sacc.) Hara, Nȏgyȏkoku [Agriculturalist]
9: 24. 1915.
? Nozemia macrospora (Sacc.) Tasugi, 1931.
Phytophthora macrospora (Sacc.) S. Ito & Tanaka, Ann.
Phytopath. Soc. Japan 10: 138. 1940.
Fig. 9. Sclerospora farlowii. A. Oospores embedded in host ssue. B, C. Oospores.
AB
C

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Graminicolous downy mildew pathogens
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73
Possible synonyms: Sclerospora oryzae Brizi, Natura, Milano 10:
168–180. 1919.
Phytophthora oryzae (Brizi) Hara, Diseases of the rice plant
[Ineno Byogai], Edn 2: 57. 1939.
Typus: Germany, Saxony, Königstein, near the Königstein Fortress,
Phlaris arundinaceae (Pooideae), 26 Aug. 1895, P. Magnus [neotype
designated here BPI 187265 (MBT 10002160); isotypes BPI 187266
(MBT 10002161), MICH00010280]. Supplementary Fig. S16 shows the
neotype BPI 187265; Supplementary Fig. S17 shows isotype BPI 187266.
Descripon: Mycelium hyaline, without septa, with haustoria,
intercellular, aggregang near vascular bundles. Sporangiophores
emerging from stomata, external hyphae (8–) 14(–28) μm long
× 1–4 μm wide; undierenated from hyphae in the host,
sympodial. Sporangia in clusters of 4–5, limoniform, obovate or
ellipsoidal, hyaline to slightly purplish, moderately papillate; 58–
98 × 30–65 μm (natural material) or (65–)87(–113) × (33–)44(–
55) μm (in water). Zoospores at rst ovate or irregularly kidney
shaped, somewhat globose when mole, spherical at rest, (13–)
11(–16) × (10–)13(–14) μm, may produce zoosporangia (10–)
13(–16) μm diam with germ tubes 1.6–2.5 μm wide. Oogonia
somewhat globose, light greenish to greenish brown, 50–95 ×
55–100 μm (mostly 57–73 × 63–75 mm) and averaging 65 × 69
μm; wall 2.5–7.5 μm thick, commonly (3.8–)4.3(–5) μm thick.
Antheridia laterally aached, hyaline to light yellow, obovate to
ellipsoidal, wall slightly thickened, (13–)15(–23) × (23–)28(–41)
μm, wall (1.8–)2.5(–3.8) μm thick. Oospores hyaline, somewhat
globose, aached closely to the wall of the oogonium (43–)
57(–70) × (43–) 60(–73) μm; wall (3.8–)6.5(–10) μm thick,
germinate indirectly by germ tube (Saccardo 1890, Tanaka 1940,
Waterhouse 1964, Fig. 8C).
Diagnosis: The morphology of the asexual stage (short,
unbranched, and undierenated sporangiophores) and the
indirect germinaon of sporangia dierenate Sclerophthora
macrospora from Sclerospora and all other Peronosporaceae
genera. Sclerophthora macrospora can be disnguished from
Sclerospora graminicola by its larger zoospores, and from
Sclerospora secalina by its hyaline, larger oospores (Waterhouse
1964).
Reference sequence data: Ex-HUH 892 nucleode sequences
KP965748 (cox2), EU826119 (28S rDNA).
Host range: This species is reported from approximately 141
Poaceae hosts globally, comprising tropical and temperate
cereals, forage grasses, turf grasses, and many weedy grasses
(Pupipat 1975, Safeeulla 1976, Farr & Rossman 2021). However,
it is possible that Sclerophthora macrospora is a species
complex (Telle et al. 2011, Telle & Thines 2012, Thines et al.
2015). Molecular phylogenec analyses of mulple isolates of
Sclerophthora macrospora from dierent hosts resolved several
disnct clades, with isolates collected from the same host
species oen falling within dierent clades (Telle & Thines 2012).
Reported hosts include Avena sava (Pooideae, Poeae), Eleusine
coracana (Chloridoideae, Cynodonteae), Festuca spp. (Pooideae,
Poinae), Hordeum vulgare (Pooideae, Triceae), Lolium spp.
(Pooideae, Poinae), Pennisetum glaucum (Pooideae, Poeae), Oryza
sava (Oryzoideae, Oryzeae), Sorghum bicolor (Panicoideae,
Andropogoneae), Tricum spp. (Pooideae, Panicoideae), Zea
mays (Panicoideae, Andropogoneae), and others (see Notes).
Notes: Sclerophthora macrospora causes diseases referred
to as either downy mildew, crazy top, or witches’ broom;
on rice the pathogen causes yellow wilt, and on turfgrass it
causes yellow tu. The pathogen has a world-wide distribuon
in temperate and warm climate regions of Africa, Asia,
Europe, the Americas, and Oceania. In Morocco and the
USA, Sclerophthora macrospora is a quaranne pest. It is
subjected to regulaons in Egypt, Paraguay, Bahrain, and two
EPPO regions due to its inclusion on the EPPO A1/A2 invasive
pest list (EPPO 2021). The pathogen is considered of minor
importance on maize, rice, sorghum, sugarcane, turfgrass, and
wheat (Smith & Renfro 2016, Lee & Groth 2018, Sugarcane
Research Australia 2019, CIMMYT 2021). However, because
of high levels of disease incidence (> 50 %) and yield losses
as high as 100 %, Sclerophthora macrospora has a signicant
economic impact on the producon of nger millet (Eleusine
coracana), pearl millet (Pennisetum glaucum), and other small
millets in Africa and Asia, especially in India (Nagaraja & Das
2016, Nagaraja et al. 2016). The most characterisc symptoms
induced by Sclerophthora macrospora are phyllody and the
development of distorted, twisted, abnormally large panicles,
tassels, or heads (Holliday 1980).
A holotype was not designated for Sclerophthora macrospora
(Saccardo 1890), and no illustraons were published with the
protolog. The protolog indicates that collecons were made in
Australia from living leaves of an unnamed species of Alopecurus
(Pooideae, Poodae), a genus that currently comprises 45 species
and also previously included species that are now members of at
least 14 dierent genera. In the absence of original materials, we
selected BPI 187265 to serve as the neotype for Sclerophthora
macrospora. BPI 187265 is one of the original collecons made
by Magnus in 1895 when he described Sclerospora kriegeriana
(Magnus 1896), a later synonym of Sclerospora macrospora
published just a few years aer Saccardo’s work (Thirumalachar
et al. 1953, Waterhouse 1964, Telle & Thines 2012).
Sclerophthora rayssiae J.A. Crouch & Thines sp. nov. MycoBank
MB 840576.
Synonym: ‘Sclerophthora rayssiae’ R.G. Kenneth et al., Bull.
Torrey Bot. Club 91: 189. 1964. [nom. inval. Art. 40.1].
Typus: illustraon in Bull. Torrey Bot. Club 91: 186, gs 1–4, 1964
(holotype designated here) based on a collecon made in Israel,
Valley of Esdraelon, Mishmar Ha-Emek, Hordeum vulgare (Pooideae,
Triceae), 24 Mar. 1958, R.G. Kenneth, Y. Koln, & I. Wahl.
Descripon: Sporangiophores very short, hyphoid, nocturnal
under natural condions. Sporangia lemon shaped or ovate,
hyaline 28.8–55.0 × 19.2–27.9 μm, base with wedge-shaped
pedicel, apex poroid and somemes protruding, granular,
infrequently germinang directly but primarily germinang
indirectly by 6–10 reniform zoospores through the apical pore.
Zoospores biagellate, 7.5 × 11.0 μm long. Oogonia usually
sinuous, unevenly thickened, 44.4–59.2(–61.4) μm diam.
Antheridia paragynous, closely appressed to oogonium. Oospores
abundant throughout mesophyll within lesions, solitary, or in
groups or clumped, not tending to congregate in any area of the
blade. Oospores globular, occasionally subglobular, light golden
amber, 29.6–44.4 (mostly 33.3) μm diam; wall deep golden
brown, smooth and thin; usually eccentrically located within
oogonial wall (Kenneth et al. 1964; Fig. 8D).

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Crouch et al.
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Prof. dr P.W. Crous,Westerdijk Fungal BiodiversityInstitute, P.O. Box 85167, 3508 AD Utrecht, The Netherlands.
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74
Reference sequence data: No sequence data available from type
material or bona de specimens.
Host range: Hordeum vulgare (Pooideae, Triceae).
Notes: Sclerophthora rayssiae was rst idened in Israel in
1958 causing downy mildew disease in elds of Hordeum
vulgare (barley). The disease recurred at the same site annually
from 1961–1963 and was considered widespread throughout
two regions of the country (Kenneth et al. 1964). Infected plants
show symptoms such as minor leaf lesions and did not induce
host deformaon (Kenneth et al. 1964). Subsequently there
have been limited reports of the pathogen (Farr and Rossman
2021). Barley downy mildew outbreaks that occurred in 2003–
2004 and 2007–2008 in India were aributed to Sclerophthora
rayssiae, but the pathogen identy cannot be readily conrmed,
as the report was limited to an abstract (Singh et al. 2009) and
did not detail the pathogen morphology. As such, we cannot rule
out the possibility that the destrucve symptomology (stunng,
chlorosis, deformaon leading to plant death) described in the
21st century Indian outbreaks might represent an outbreak of
crazy top caused by Sclerophthora macrospora (Miles and Epps
1942, Oswald and Houston 1951) because the symptomology
diers greatly from the descripons of Sclerophthora rayssiae
as a weak pathogen on the same host (Kenneth et al. 1964).
A type specimen was not designated but was required at
the me of publicaon; therefore, Sclerophthora rayssiae R.G.
Kenneth was not validly published (1964). Kenneth’s collecon at
HUJ, including his specimen of this species, is thought to be lost.
However published illustraons of the original material clearly
depict the diagnosc features and are used as the holotype for
the newly validated species.
Sclerophthora zeae J.A. Crouch & Thines, sp. nov. MycoBank
MB 840577.
Synonym: ‘Sclerophthora rayssiae var. zeae’ Payak & Renfro,
Phytopathol. 57: 395. 1967. [nom. inval. Art. 35.1].
Typus: India, Pantnagar (U. P.), Zea mays var. indurate (Panidoideae,
Andropogoneae), 12 Oct. 1965, M.M. Payak & B.L. Renfro (holotype
designated here, HCIO 29038).
Descripon: Sporangiophores short, hyphal. Sporangia ovate,
obclavate, ellipc, hyaline, 29.0–66.5 × 18.5–26.0 μm, smooth-
walled, poroid apex truncate or rounded, with a persistent,
straight or curvate peduncle, producing 4–8 zoospores.
Zoospores spherical, hyaline, 7.5–11.0 μm diam. Oogonia
subglobose, hyaline to light straw-colored, 33–44.5 μm diam,
thin-walled, with 1–2 paragynous antheridia. Oospores spherical
or subspherical, hyaline, 29.5–37.0 μm diam; wall smooth
and glistening, 4 μm thick, wall conuent with oogonial wall;
contents include prominent oil globule; centrally located in the
oogonium (Payak & Renfro 1967; Fig. 8E).
Diagnosis: The large size of Sclerophthora zeae zoospores
(7.5–11.7 μm long), as with Eraphthora butleri, Sclerophthora
lolii, and Sclerophthora rayssiae, is disncve among the
Peronosporaceae (Kenneth et al. 1964, Payak & Renfro 1967).
Parasic to Zea mays, which dierenates it from the host
range of all other Sclerophthora species with the excepon of
Sclerophthora macrospora. Diers from Sclerophthora rayssiae
based on the following morphological characters: smaller
oogonia (33.0–44.5 μm vs. 44.4–59.2 μm for Sclerophthora
rayssiae) with thin even walls (versus the sinuous, unevenly
thickened walls of Sclerophthora rayssiae); the absence of
the golden to amber brown oogonia and oospores exhibited
by Sclerophthora rayssiae; a sporangial shape that is obovate,
obclavate, or ellipc,
Reference sequence data: No sequence data available from type
material or bona de specimens.
Host range: Digitaria bicornis, Digitaria sanguinalis (Panicoideae,
Panicodae); Zea mays (Panicoideae, Andropogoneae).
Notes: Payak & Renfro (1967) rst documented the causal agent
of brown stripe downy mildew of maize as Sclerophthora rayssiae
var. zeae, which was collected from severe disease outbreaks
that occurred throughout several regions of India in the early
1960s. The pathogen is not known from outside India. Disease
symptoms are disnct from those caused by Sclerophthora
macrospora, in that leaf shredding and deformaon are not
observed (Payak & Renfro 1967). Only the leaves are infected
and show narrow vein-delimited chloroc stripes parallel to
the vascular ssue with well-dened margins that eventually
became reddish brown to purple (Galgóczy et al. 2014).
Brown stripe downy mildew can result in maize yield losses
between 20–100 % depending on culvar suscepbility and
weather (Putnam 2007). In present day India, the disease is
of minor importance compared to other maize diseases and is
generally adequately controlled using culvar resistance and
chemical applicaons (B.M. Prassa and Sujay Rakshit, pers.
comm.; Lal et al. 1980, Basadrai et al. 2002, Singh & Singh 2012).
In the USA, this pathogen is regulated under strict quaranne
protocols as a USDA-APHIS Select Agent because it is considered
a signicant potenal threat to the country’s agricultural
security.
Sclerophthora rayssiae var. zeae Payak & Renfro was not
validly published, as it was based on the invalid basionym
Sclerophthora rayssiae R.G. Kenneth (Art. 35.1, Turland et al.
2018). This provides us with a unique opportunity to revisit the
taxonomy of the organism from a modern perspecve, given the
narrow species concept that we now recognize as the primary
evoluonary trajectory for downy mildew pathogens (Gäumann
1918, 1923, Gustavsson 1959). In their decision to describe
the organism as a variety and not assign the rank of species,
Payak & Renfro adopted a broad species concept in assigning a
taxonomic rank that was consistent with the accepted pracce
of the me and in line with the approach of most applied plant
pathologists (de Bary 1863, Yerkes & Shaw 1959). Payak & Renfro
(1967) were of the opinion that the host dierences between
the two organisms were not sucient evidence to warrant the
delimitaon of a new species. However, Payak & Renfro also
acknowledged several morphological features and the diering
host range of Sclerophthora rayssiae, parasic of the cool-season
grass Hordeum vulgare (Pooideae), and Sclerophthora zeae,
which is parasic of warm-season Panidoideae grasses. Based
on diagnosable morphological dierences and host range, we
treat this organism as a separate species rather than a varietal
form of Sclerophthora rayssiae.
Sclerospora J. Schröt., Hedwigia 18: 86. 1879.
Synonyms: Sclerospora subgen. Sclerospora, Hedwigia 18: 86.
1879.

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Graminicolous downy mildew pathogens
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Prof. dr P.W. Crous,Westerdijk Fungal BiodiversityInstitute, P.O. Box 85167, 3508 AD Utrecht, The Netherlands.
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75
‘Sclerospora subgen. Eusclerospora’, Bot. Mag., Tokyo 27: 218.
1913. [nom. nud., Art. 21.3, 22.2]
Sclerospora subgen. Sclerospora J. Schröt., Hedwigia 18: 86.
1879. [nom. nud., Art. 22.1]
Type species: Sclerospora graminicola (Sacc.) J. Schröt., in
Cohn, Krypt.-Fl. Schlesien (Breslau) 3.1(9–16): 236. 1886 [1889].
Descripon: Sporangiophores sy upright with sparse straight
branches. Sporangia ovate, with a papilla at the apex, forming
zoospores. Oospores spherical with very thick, mul-layered,
brown wall that fuses with the skin of the oogonium (Schröter
1886).
Notes: Sclerospora was the rst Peronosporaceae genus
specically erected to accommodate a grass parasite, and the
type species Sclerospora graminicola was the rst graminicolous
downy mildew pathogen ever described, albeit three separate
mes (Shaw 1975). Members of the genus are diagnosed
through their asexual structures – the sporangial producon of
zoospores, evanescent sporangiophores with mulple branches,
and a sporangial papilla – morphological traits that uniquely
disnguish members of the genus from other Peronosporaceae.
In pracce, idencaon of the Sclerospora is dicult to
achieve based on morphological features alone, given the
evanescent nature of the diagnosc asexual stage. Sclerospora
sporangial structures are formed nocturnally in the presence of
dew on living host material, persist only for a few hours to days,
and nally collapse, desiccate, and/or gelanize aer zoospore
discharge (Kenneth 1970, Jeger et al. 1998). This means that
asexual structures are oen not preserved on herbarium
materials or other dried specimens, liming their value for
idencaon and taxonomic study. Given the destrucve
nature of Sclerospora graminicola parasizing the staple food
crops pearl millet and foxtail millet (Pennisetum glaucum,
Setaria italica) this fundamental limitaon carries important
implicaons for detecng, prevenng, and quaranning downy
mildew disease on millet crops globally.
Currently, Sclerospora contains ve validly described
species and is unique among the graminicolous downy mildew
genera in that three dierent host subfamilies are parasized.
However, our understanding of Sclerospora species boundaries
and host associaon within the genus is poorly dened. The
generic identy of Sclerospora farlowii, Sclerospora iseilemas,
Sclerospora northii, and Sclerospora secalina is not reliable at
present, as these species were all described as members of the
genus Sclerospora based on oogonial structures, in the absence
of diagnosc asexual characters. However, the oogonial morph of
these species shares common features: oogonia and oospores are
generally dark colored, spherical to sub-globose, with thick, mul-
layered oogonial walls fused to the oogonia (Schröter 1886).
For species-level discriminaon of Sclerospora, a combinaon
of morphological and host range characters is the only approach
currently available. However, the globally distributed, broad-
host-range type species Sclerospora graminicola appears to be
a species complex, with 198 records of the pathogen reported
from 20 species of Poaceae (Farr & Rossman 2021). It is
conceivable that many graminicolous downy mildew outbreaks
were aributed to Sclerospora graminicola based on insucient
evidence or simply because the species was one of just a few
downy mildew pathogens known from Poaceae hosts during the
late 19th and early 20th centuries.
Unl the taxonomy of this genus can be further studied and
resolved, it is clear that accurate diagnosis of Sclerospora species
is a daunng task. Molecular phylogenec research across host
populaons and incorporang type materials will be required to
provide a basic framework to support idencaon, diagnoscs,
and taxonomic resoluon of the Sclerospora.
Sclerospora farlowii Griths, Bull. Torrey Bot. Club 34: 207.
1907.
Synonyms: ‘Sclerophthora farlowii’ (Griths) R.G. Kenneth,
Israel J. Bot. 12: 139. 1963 [1964]. [nom. nud., Art. 36.1, 39.1]
‘Sclerophthora farlowii’ (Griths) R. G. Kenneth, Phytoparasica
7: 50. 1964. [nom. nud., Art. 36.1, 39.1]
Typus: USA, Arizona, Cochise, Chloris virgata (as Chloris elegans;
Chloridoideae, Cynodonteae), Oct. 1900, D. Griths [lectotype
designated here, BPI 187077 (MBT 10002162); isotypes BPI 187076,
BPI 187078, FH 965329, FH 1093687 (MBT 10002163)]. Supplementary
Fig. S18 shows the lectotype BPI 1187077. Supplementary Figs S19 and
S20 show isotypes BPI 187076 and BPI 187078.
Descripon: Oospores sub-globose, deep dark reddish brown
and oen appearing black and opaque, 28–45 μm diam. Asexual
morph not observed. (Griths 1907; Figs 9, 10A).
Diagnosis: Sclerospora farlowii produces sub-globose, deep dark
reddish-brown oospores that oen appear black and opaque
and parasizes Chloris virgata, which taken together are unique
features for Peronosporaceae parasizing hosts in the Poaceae
family. Peronosclerospora miscanthi and Peronosclerospora
noblei also produce dark reddish to amber brown oospores of
similar diam to those of Sclerospora farlowii, but these species
dier by their globose-shaped oospores versus the sub-globose
oospores of Sclerospora farlowii and by their host range, which
is limited to Andropogoneae hosts.
Reference sequence data: No sequence data available from type
material or bona de specimens.
Host range: Chloris virgata (Chloridoideae, Cynodonteae);
possible reports on Cynodon dactylon (Chloridoideae,
Cynodonteae); Deyeuxia sp. (Poaceae, Pooideae).
Notes: Griths (1907) noted that Sclerospora farlowii was one of
the most common “fungi” encountered in southern Arizona being
locally abundant but with lile to no discernable impact on the
health of the infected host plants. The type host, Chloris virgata
(feather ngergrass), is nave to the Americas. It is most notable
as a highly adaptable, prolic weed in numerous ecosystems and
an aggressive invasive plant outside its nave range.
The reports of Sclerospora farlowii on Cynodon dactylon and
Deyeuxia sp. from checklist publicaons (Farr & Rossman 2021)
need further invesgaon. Given that most Peronosporaceae
species are highly specialized and their taxonomy follows a
narrow species concept (e.g., García-Blázquez et al. 2008,
Thines & Choi 2016, Petrželová et al. 2017), it seems unlikely
that these hosts from three dierent plant genera with dierent
photosynthec pathways are parasized by Sclerospora farlowii.
There are also several smuts that parasize Deyeuxia species
that could potenally be mistaken for the resng spores of a
sclerospora-like species (Vánky & Guo 2001), as was the case
when Sclerospora graminicola was mistakenly brought into

© 2022 Westerdijk Fungal Biodiversity Instute
Crouch et al.
Editor-in-Chief
Prof. dr P.W. Crous,Westerdijk Fungal BiodiversityInstitute, P.O. Box 85167, 3508 AD Utrecht, The Netherlands.
E-mail:p.crous@westerdijkinstitute.nl
76
Fig. 10. A. Sclerospora farlowii, oogonium (arrow) and oospores B. Sclerospora graminicola, sporangiophore, sporangia, including a close-up of a
cytoplasm-lled sporangium and an empty sporangium (inset); oospores, including an oospore germinang to produce a sporangium (arrow). C.
Sclerospora iseilemas, oospores. D. Sclerospora northii, oospores, one in surface view (arrow). E. Sclerospora secalina, oogonium with antheridium
(arrow) and oospores in various stages of maturity. Illustraons were prepared from published reference images in Weston (1924, 1929), Howe
(1930), Naumov (1949), Thirumalachar & Narasimhan (1949), Pande (1972), and Thakur et al. (2011).

© 2022 Westerdijk Fungal Biodiversity Instute
Graminicolous downy mildew pathogens
Editor-in-Chief
Prof. dr P.W. Crous,Westerdijk Fungal BiodiversityInstitute, P.O. Box 85167, 3508 AD Utrecht, The Netherlands.
E-mail:p.crous@westerdijkinstitute.nl
77
connecon with the smut species Uslago urbani (Waterhouse
1964, Shaw 1975).
In some publicaons, Sclerospora farlowii is listed under the
name Sclerophthora farlowii (Griths) R.G. Kenneth (Kenneth
1981, Dick 2001, 2013, Spencer & Dick 2002). At the me of
this wring (September 2021), MycoBank and Index Fungorum
give the current name as Sclerophthora farlowii (Griths) R.G.
Kenneth, Israel J. Bot.: 139. 1964. However, a publicaon by R.G.
Kenneth in the Israel Journal of Botany from the year 1964 does
not exist. A publicaon by R.G. Kenneth from 1963 in the Israel
Journal of Botany does exist, and on page 139, one nds the
diagnosis of Sclerophthora lolii R. G. Kenneth sp. nov., but not
Sclerophthora farlowii (Griths) R. G. Kenneth comb. nov. The
rst published menon of Sclerophthora farlowii (Griths) R.G.
Kenneth dates to 1979 (Kenneth 1979), in a scienc meeng
abstract that states that examinaon of the Sclerospora farlowii
herbarium material supports the hypothesis that the species
should be transferred to Sclerophthora. Based on annotaon
labels in the Farlow Herbarium, these examinaons took place in
1978. However, Sclerophthora farlowii (Griths) R. G. Kenneth
is invalid under ICN Art. 36.1 and Art. 39.1 (Turland et al. 2018).
The original species descripon for Sclerospora farlowii
is brief and limited to a descripon of oospore morphology.
In Kenneth’s 1979 meeng abstract, host range was cited as
juscaon for transfer of Sclerospora farlowii to Sclerophthora,
along with unspecied “sporangia and hyphoid sporangiophore”
features, but host range is not a dening trait for the genus
Sclerophthora and no details were provided about morphological
characters. Overall, addional research is required to resolve
any taxonomic uncertainty surrounding the generic identy of
Sclerospora farlowii.
Griths did not designate a holotype for Sclerospora
farlowii, although it was not required at the me of publicaon
(Griths 1907). The original collecons were distributed to BPI
and FH, and in Grith’s personal herbarium (Griths 1907).
Examinaon of the BPI collecons idened specimen BPI
187077, BPI 18076, and BPI 187078 with the same collecon
details described by Grith’s, with notes wrien in W.H.
Weston’s handwring that these were type material. BPI 187077
is herein used to lectotypify the species.
Sclerospora graminicola (Sacc.) J. Schröt., in Cohn, Krypt.-Fl.
Schlesien (Breslau) 3.1(9–16): 236. 1886.
Basionym: Protomyces graminicola Sacc., Mycotheca Vene 5:
no. 496. 1876.
Synonyms: Uslago (?) urbanii Magnus [as ‘urbani’], Verh. Bot.
Ver. Prov. Brandenb. 20: 52. 1878.
Sclerospora graminicola (Sacc.) J. Schröet., Hedwigia 18: 86.
1879.
Peronospora setariae Pass., Grevillea 7: 99. 1879.
Peronospora graminicola (Sacc.) Sacc., Michella 2: 586. 1882.
Sclerospora graminicola var. setariae-italicae Traverso, Boll. Soc.
Bot. Ital. 1902: 1968. 1902.
Sclerospora graminicola var. graminicola Kulk., Memoirs of the
Dept. Agric. India, Bot. Ser. 55: 272. 1913.
‘Sclerospora graminicola’ Schröter apud Oudemans, Enum. Syst.
Fungi. 1: 719. 1919. [nom. inval. Art 32.1(c)]. A slip of the pen for
Peronospora graminicola (Sacc.) Sacc.
‘Sclerospora setariae-italicae’ (Traverso) Cif. & Sousa da Cȃmara,
Quad. Ist. Bot. Uni. Pavia 30: 233. 1963. [nom. inval., Art. 41.1]
Typus: Poland, Liegnitz, Waldau, Breslau, Setaria viridis, date unknown,
W.G. Schneider, Herbarium Schlesischer Pilze: 553.
Descripon: Sporangiophores evanescent, nocturnal, erect,
100 × 12–15 µm; branched in the lower part but usually
with a few short, thick branches that are dichotomously or
trichotomously formed at the top and crowned with numerous
ulmate branchlets on which sporangia are borne. Sporangia
hyaline, subglobose to ellipcal, slightly pointed at the free end,
with a thin smooth wall; rapidly germinate in water, liberang
zoospores in variable numbers, from three to four and up to a
dozen or more zoospores per sporangium depending on size.
Zoospores irregularly kidney shaped, unequal-sided, aened
bodies, 9–12 μm diam, forming two oppositely directed agella
on the concave side, and germinang via hyphae. Oogonia
ellipcal, angular or irregular shape due to irregularly thickened
wall, tawny to brown or chestnut brown, (34–)42(–52) μm diam;
wall irregular with thickened areas and conspicuous ridges, 4–11
µm, somemes up to 17 µm thick, making the whole spore, thus,
33–45 μm (somemes up to 50 μm) diam. Oospores spherical,
yellow (Chromotaxia), (22.5–)32(–35) μm diam; wall evenly
thickened, smooth. (Butler 1907, Schröeter 1886; Fig. 10B).
Diagnosis: Evanescent sporangiophores with mulple branches
bearing sporangia uniquely disnguish Sclerospora graminicola
from members of the Peronosporaceae outside of the genus
Sclerospora. Diers from Sclerospora iseilemas, and Sclerospora
secalina by having an oogonial wall with conspicuous ridges.
Diers from Sclerospora northii by having smaller oogonia (41
µm diam versus 51–61 µm diam, respecvely).
Reference sequence data: Ex-HV532 nucleode sequences
DQ365768 (cox2), AY035514 (28S rDNA D1/D2/D3), AY273987
(28S rDNA D7/D8).
Host range: Setaria spp. and Pennisetum glaucum (Panicoideae,
Paniceae). Globally, the species is also reported as a parasite of
20 species of Poaceae in two subfamilies including 13 genera:
Beckeropsis, Digitaria, Echinochloa, Euchlaena, Panicum,
Pennisetum, Setaria, Sorghum, Zea (Panicoideae); Alopecurus,
Dactylis, Holcus, and Tricum (Pooideae) (Weston & Weber 1928,
Farr & Rossman 2021). As discussed in the Notes secon below, the
true host range and impact of this species may be limited to Setaria
spp. or even the type host Setaria viridis (wild foxtail millet).
Notes: Sclerospora graminicola reportedly impacts producon
of two widely culvated staple human food crops signicantly:
pearl millet (Pennisetum glaucum) and foxtail millet (Setaria
italica; Safeeulla 1976, Francis & Williams 1983, Kumar et al.
2012). Pearl millet in Africa and Asia are the most aected by
Sclerospora graminicola, with losses of 20–100 % reported
(Kumar et al. 2012). Crop losses in foxtail millet can range
between 20–70 % (Li et al. 2020). To date, pearl millet has not
been reported as a host in the Americas (Francis & Williams
1983, Kumar et al. 2012, K.M. Devos, pers. comm.).
There are mulple lines of evidence that suggest Sclerospora
graminicola is a species complex in need of careful taxonomic
evaluaon, parcularly across host populaons (M. Thines,
unpubl. data). Broadly speaking, since most Peronosporaceae
species are specialized to parasism of a single or only a few host
species, records of this species as a broad-host range pathogen of
13 dierent genera across two plant families are inconsistent with

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Crouch et al.
Editor-in-Chief
Prof. dr P.W. Crous,Westerdijk Fungal BiodiversityInstitute, P.O. Box 85167, 3508 AD Utrecht, The Netherlands.
E-mail:p.crous@westerdijkinstitute.nl
78
expectaons for the species (e.g., Thines & Choi 2016, Petrželová
et al. 2017). More specically, most – but not all – experimental
evidence from host range studies points to the disncon
between Sclerospora graminicola strains that infect pearl millet
from those that infect Setaria spp., including foxtail millet (Melhus
et al. 1928, Safeeulla 1976, Francis & Williams 1983, Singh et al.
1993). Since Sclerospora graminicola isolates from pearl millet
are heterothallic with two mang types (Michelmore et al. 1982,
Idris & Ball 1984), the inability of strains from Setaria spp. to infect
pearl millet could indicate that the lineage(s) on Setaria spp. are
reproducvely isolated from the lineages on pearl millet, which
sases the separaon of the two lineages into two species under
a biological species concept. Molecular studies of Sclerospora
graminicola are very limited, with only a few specimens from
pearl millet analyzed using cox2 and 28S rDNA sequence data
(Thines et al. 2008, Telle et al. 2011, Thines et al. 2015), although
the availability of whole genome sequence data (Nayaka et al.
2017) may lead to new invesgaons of species diversity.
Sclerospora iseilemas Thirum. & Naras., Indian Phytopathol.
2: 49. 1949.
Typus: India, Mysore, Nandi Hills, Iseilema prostratum (as Iseilema
laxum; Panicoideae, Andropogoneae), 20 Jan. 1947, M.J. Narasimhan &
H.C. Govindu [lectotype designated here BPI 187262 (MBT 10002239);
isotype IMI 38399 (MBT 10002240)]. Supplementary Fig. S21 shows the
lectotype BPI 187262.
Descripon: Oogonia sub-globose to spherical, pale golden-
yellow, 43–61 µm diam; wall deeply folded, tuberculate, almost
spiny, 5.5 µm thick. Antheridia 2–5, conoid to triangular, 27–40 ×
15.5–27 µm, persistent in mature oospore. Oospores spherical,
hyaline, 38–50 µm diam, pleroc, inner contents granular and
enclosing a few droplets; wall 3–3.5 µm thick, conuent with
the oogonial wall. Asexual morph not observed (Thirumalachar
& Narasimhan 1949; Fig. 10C).
Diagnosis: Parasizes the same host as Peronosclerospora westonii,
but can be dierenated by oospore size, with the spherical, pale
oospores of Sclerospora iseilemas measuring 38–50 µm diam
with tuberculate endosporium walls 3.0–3.5 µm thick versus the
spherical golden-brown oospores of Peronosclerospora westonii
measuring 23–29 µm diam with smooth endosporium walls
6–9 µm thick. Diers from Sclerospora graminicola, Sclerospora
northii, and Sclerospora secalina by having a tuberculate, almost
spiny oogonial wall. Diers from Sclerospora farlowii by its
parasism of Iseilema prostratum.
Reference sequence data: Ex-lectotype nucleode sequences
OK185342 (cox2), OK255493 (28S rDNA).
Host range: Known only from the type host Iseilema prostratum.
Notes: Sclerospora iseilemas has not been reported since its
original descripon in 1949, when a single eld of Iseilema
prostratum (musal grass) with downy mildew disease symptoms
was documented in India (Thirumalachar & Narasimhan 1949).
The type host is nave to the Indian subconnent and parts
of South-East Asia, but the extent to which the pathogen is
distributed with the host is unknown. Sclerospora iseilemas
infecons result in witches-broom-like inorescences with
reduced internodal elongaon and excessive proliferaon and
branching of the spikelets. Although oogonia producon is
heavy within the mesophyll of infected leaves, no leaf shredding
symptoms occur, and leaf symptoms are limited to chlorosis
(Thirumalachar & Narasimhan 1949).
Since Thirumalachar & Narasimhan (1949) only observed the
oogonial morph, it is impossible to conclude from morphological
data alone that Sclerospora iseilemas is a member of the
genus Sclerospora. The basic morphological features that dene
Sclerospora are only found in the sporangia: namely, through
the evanescent producon of sporangiophores with mulple
branches, and the sporangial producon of zoospores that
escape through a pailla.
A holotype specimen was not designated in the protolog,
although collecon details were listed, followed by the word
“type.” BPI contains a specimen of Sclerospora iseilemas (BPI
187262) with collecon details matching those given in the
protolog and marked “type” on the outer envelope and as part
of the enclosed handwrien annotaons; we therefore use this
specimen to lectotypify the species.
Sclerospora northii W. Weston [as ‘nothi’], Phytopathol. 19: 965.
1929.
Synonym: ‘Sclerophthora northii’ (W. Weston) Thirum. et al.,
Bull. Torrey Bot. Club 80: 300. 1953. [nom. nud., Art. 36.1, 39.1]
Typus: Fiji Islands, Suva, Rarawai Estate, Saccharum maximum (as
Erianthus maximus var. seemanii; Panicoideae, Andropogoneae), 23
Jun. 1924, H.F. Clarke [lectotype designated here BPI 187307 (MBT
10002241), isotype FH 965380 (MBT 10002242)]. Supplementary Fig.
S22 shows the lectotype BPI 187307.
Descripon: Oogonia rounded polyhedral with several aened
faces bordered by ridges, occasionally irregular, elongate pyriform,
or unequally rounded oblong, amber brown (somemes raw
sienna to argus brown), 40–70 µm (up to 57–60.9 µm × 51–56.9
µm) diam; wall with arched irregular, ridged prominences, 3–5 µm
(occasionally to 10 µm); remains of oogonial stalk or antheridium
rare. Oogonia spherical, hyaline to pale amber, 39–46.9 µm (mode
41–44.9 µm; up to 35–52 µm) diam, contents nely granular with
denser aggregaons, central area usually clear with occasionally
one or more oil globules; wall dense, smooth, homogeneous
to indisnctly lamellate, 2–4.5 µm thick. Asexual morph not
observed. (Weston 1929b; Fig. 10D).
Diagnosis: Disnguished from Peronosclerospora miscanthi,
Peronosclerospora spontanea and Peronosclerospora sacchari,
which also parasize Saccharum spp., due to the producon of
oospores each enclosed in a darkened, thickened oogonial wall
with several aened polyhedral faces. Diers from Sclerospora
iseiliemas and Sclerospora secalina by having an oogonial
wall with conspicuous ridges and by parasism of Saccharum
maximum. Diers from Sclerospora graminicola by having larger
oogonia (51–61 µm diam vs. 41 µm diam, respecvely). Diers
from Sclerospora farlowii by parasism of Saccharum maximum.
Reference sequence data: No sequence data available from type
material or bona de specimens.
Host range: Known only from the type host Saccharum maximum
Panicoideae, Andropogoneae.
Notes: Sclerospora northii was reported as a pathogen of
Saccharum maximum, a nave reed-like grass common in Fiji

© 2022 Westerdijk Fungal Biodiversity Instute
Graminicolous downy mildew pathogens
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Prof. dr P.W. Crous,Westerdijk Fungal BiodiversityInstitute, P.O. Box 85167, 3508 AD Utrecht, The Netherlands.
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79
(Weston 1929). Infected plants were dried and brown with
shredded leaves (Weston 1929). The pathogen has not been
reported since the original 1924 sighng, and it is unknown
what impact Sclerospora northii has on host populaons.
At the me of wring (September 2021), Index Fungorum
listed the current name for this species as ‘Sclerophthora northii’
(W. Weston) Thirum. et al., Bull. Torrey Bot. Club 80: 300. 1953.
However, the correct name for this pathogen is Sclerospora
northii W. Weston. The publicaon cited for “Sclerophthora
northii,” in which the genus Sclerophthora was rst described,
did not make a new combinaon for Sclerospora northii, and the
species was not menoned at any point in the arcle.
As discussed by Shaw (1978), the asexual morph of this
pathogen has not been observed. Sclerospora northii was
one of ve Sclerospora species that were not transferred to
Peronosclerospora by Shaw (1978), as the absence of any record
of asexual reproducve structures precluded assignment to
either Peronosclerospora or Sclerospora.
Fig. 11. Viennoa oplismeni, sporangiophore, with close-up of indeterminant sporangiophore ps (top inset) and helical haustoria (boom inset).
Illustraons were prepared from published reference images in Goker et al. (2007).

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Crouch et al.
Editor-in-Chief
Prof. dr P.W. Crous,Westerdijk Fungal BiodiversityInstitute, P.O. Box 85167, 3508 AD Utrecht, The Netherlands.
E-mail:p.crous@westerdijkinstitute.nl
80
Weston did not designate a holotype for Sclerospora northii;
however, he provided detailed collecon data regarding his
materials. BPI and FH holdings that originate from Weston’s
collecons includes specimens BPI 187307 and FH 965380 with
idencal collecon data as that which is communicated in the
protolog, detailed in Weston’s handwring, and is wrien on a
label from the Herbarium of W. H. Weston. These specimens are
undoubtably part of Weston’s original specimen collecon used
for describing the species; BPI 187307 is here used to lectotypify
Sclerophthora northii.
Sclerospora secalina Naumov, Notul. Syst. Sect. Cryptog. Inst.
Acad. Sci. USSR 6: 79. 1949.
Typus: Non designatus.
Descripon: Oogonia sub-spherical, 33–38 [or 48] µm diam; wall
smooth without tubercules or ridges. Antheridia 14.7 × 18 µm
diam. Oospores spherical, deep ocher, then brown, 31–46 [or
36] µm diam at maturity; wall smooth. (Waterhouse 1964; Fig.
10E).
Diagnosis: Disnct from Sclerophthora macrospora parasizing
Secale cereale by oospore size and coloraon, which are much
smaller in Sclerospora secalina (versus a diam of 62.5 µm or
more and hyaline oospores of Sclerophthora macrospora).
Diers from Sclerospora iseilemas, Sclerospora graminicola,
and Sclerospora northii by having a smooth oogonial wall
without tubercules or ridges. Diers from Sclerospora farlowii
by parasism of Secale cereale.
Reference sequence data: No sequence data available from type
material or bona de specimens.
Host range: Secale cereale (Pooideae, Tricaceae).
Notes: According to Farr & Rossman (2021), this species has
not been reported since its inial descripon as a parasite of
Secale cereale (cereal rye) in the former USSR during 1942
(Waterhouse 1964). Since Naumov only observed the oogonial
morph (Waterhouse 1964), the generic status of Sclerospora
secalina is not clear. In the absence of sporangial features and/
or molecular data, it is not possible to conclude with certainty
that this species is a member of the genus Sclerospora.
Viennoa J.A. Crouch & Thines, gen. nov. MycoBank MB 840578.
Synonym: ‘Viennoa’ Göker et al. [nom. inval. Art. 35.1]
Type species: Viennoa oplismeni J.A. Crouch & Thines
Descripon: Canad. J. Bot. 81: 682. 2003. Haustoria hyaline,
hyphoid, intracellular, long, oen ghtly coiled and slender.
Sporangiophores hyaline, monopodially branched, with
ulmate branches that are straight to slightly curved. Parasic
to members of the Poaceae (Göker et al. 2003).
Diagnosis: Diers from all other graminicolous downy
mildews in sporangiophores that show recurrent
outgrowth aer sporangia have been shed (Thines 2009).
Notes: The genus Viennoa was based on an invalid basionym
without type specimen (see notes on Viennoa oplismeni,
below), rendering it invalid itself (Art. 40.1) Hence, the genus
could not be described by reference to the type species (Art.
10.1), as it was not validly published, invalidang the genus
descripon. Therefore, we validate the genus name and the
type species here.
Viennoa oplismeni J.A. Crouch & Thines, sp. nov. MycoBank
MB 840579.
Synonyms: ‘Plasmopara oplismeni’ Vienn.-Bourg., Bull. Soc.
Mycol. France 75: 33. 1959. [nom. inval. Art. 40.1].
‘Viennoa oplismeni’ (Vienn.-Bourg.) Göker et al., Canad. J. Bot.
81: 682. 2003. [nom. inval. 35.1].
Typus: Guinea, near Kindia, on leaves of Oplismeni hirtellus (Panicoideae,
Panicodae), 3 Nov. 1963, J. Kranz (holotype GZU 335974 designated
here, isotypes BPI 784624, IMI 103944). Supplementary Fig. S23 shows
the isotype BPI 784624.
Descripon: Haustoria intracellular, hyphoid, slender, long and
oen ghtly coiled. Sporangiophores hyaline, monopodially
branched, 180–230 × 6–8 µm; branching in the upper third
into spreading branches; terminal branches straight to slightly
curved divided at right angles into short ramicaons with
swellings typically carrying three sterigmata; sterigmata bloated
and pinched, 14–23 µm long. Sporangia 14–28 × 11–17 µm.
Oogonia not observed (Figs 11, S23).
Diagnosis: Diers from other Peronosporaceae by parasizing
Oplismeni spp. Diers from Poakatesthia pennise by having
globular citroform sporangia, shorter and dichotomously
branched sporangiophores, and larger ulmate branchlets.
Diers from Graminivora graminicola by 28S DNA sequences
and, by successive outgrowth of the ulmate branchlets aer
sporangia have been shed, a feature that also disnguishes the
species from all other graminicolous downy mildews.
Reference sequence data: Ex-holotype nucleode sequences
AY035527 (28S rDNA D1/D2/D3), AY273977 (28S rDNA D7/D8).
Host range: Oplismeni hirtellus, Oplismeni compositus
(Panicoideae, Panicodae).
Notes: Reported just twice, on Oplismeni hirtellus (basketgrass)
and Oplismeni compositus (running mountaingrass) from
Guinea (Viennot-Bourgin 1959, Kranz 1965). The rst report
of the species did not list any symptoms associated with the
host infecon, but Kranz (1965) documented leaves that were
streaked yellow and rapidly roed. Although both hosts have a
cosmopolitan distribuon across most tropical and subtropical
parts of the world, Viennoa oplismeni has not been reported
since 1963 (Kranz 1965); therefore, it is unknown if the species
has any impact on host populaons.
Plasmopara oplismeni was not validly published, as a
type was not designated as required at the me, meaning
that Viennoa oplismeni (Vienn.-Bourg.) Göker et al. and the
genus Viennoa Voglmayr et al. were not validly published
(Art. 10.1, 40.1, Turland et al. 2018). It is unknown if Viennot-
Bourgin’s collecons from 1955 are extant, and no illustraons
of the species were provided (Viennot-Bourgin 1959). Duplicate
collecons of Kranz’ materials are held at BPI, GZU, IMI (K) (det.
G.M. Waterhouse, conf. H. Vogelmayr); these specimens were
made from the same host in the same locale where Viennot-

© 2022 Westerdijk Fungal Biodiversity Instute
Graminicolous downy mildew pathogens
Editor-in-Chief
Prof. dr P.W. Crous,Westerdijk Fungal BiodiversityInstitute, P.O. Box 85167, 3508 AD Utrecht, The Netherlands.
E-mail:p.crous@westerdijkinstitute.nl
81
Bourgin made collecons. GZU 335974 was studied by Göker
et al. (2003) when they designated the genus Viennoa, and it
has been characterized through morphological and molecular
analysis (Kenneth & Kranz 1973, Riethmüller et al. 2002, Göker
et al. 2003, Thines et al. 2006, Thines 2009). This specimen is
therefore designated as the holotype for Viennoa oplismeni.
DISCUSSION
Graminicolous downy mildews are predominantly tropical or
subtropical, with only two of the seven genera, Sclerophthora and
Sclerospora, extending into cool temperate climates (Spencer &
Dick 2002, Davis & Crouch 2022a, b). As most tropical ecosystems
are generally understudied, our current knowledge of the GDMs
is restricted to species occurring on crops and some anecdotal
reports from wild grasses (Waterhouse 1964, Shaw 1975, this
paper). Interesngly, maize seems to be highly suscepble to a
variety of GDM species (Kenneth 1989), and descripons of some
species, such as Peronosclerospora maydis and Peronosclerospora
philippinensis are based on infecons on this host. However,
maize is not nave to the natural range of Peronosclerospora,
suggesng that the high suscepbility of maize is because of a
naivity to downy mildew pathogens (Thines 2014), in line with
the hypothesis that host suscepbility increases with increasing
geographic distance from potenal pathogens (Thines 2019). As
maize is not nave to Asia, the natural host reservoir may be in
indigenous grasses. Because naturally occurring infecons of wild
and weedy grasses have not been systemacally studied, the
original source of inoculum is unknown for most species aecng
maize, complicang phytosanitary measures. Only recently has
a nave host has been idened for Peronosclerospora maydis
(Suharjo et al. 2020). Thus, studies of the GDMs in unmanaged
habitats are highly warranted.
Although we treat the GDMs as a group in this review,
it is unclear if the Peronosporaceae aecng grasses are
monophylec. So far, three potenally monophylec groups
have been idened from Poaceae hosts – the graminicolous
downy mildews with lasng sporangiophores (Graminivora,
Poakatesthia, and Viennoa), a group comprising Eraphthora
and Sclerophthora, and the graminicolous downy mildews with
evanescent sporangiophores (Baobabopsis, Peronoscleropsora,
Sclerospora). The relaonships of these groups remain unclear
(Thines 2014), as well as how the other downy mildew genera are
related to them. Thines (2009) hypothesized that, due to some
plesiomorphic characters and a high degree of morphological
variaon, the evoluon of downy mildews might have started
out from graminicolous hosts, but as mulgene phylogenec
data are lacking for most GDMs, this hypothesis has not yet
been tested. In any case, the phytophthora-like species aecng
sedges that are unculturable and have been placed in a genus
of their own, Kawakamia, should be included in studies of these
organisms, even though the independence of Kawakamia on
the genus level was doubted in the most recent monograph
of Phytophthora (Erwin and Ribeiro 1996). In addion,
several sclerophthora-like species that share morphological
similaries with Kawakamia, including Sclerophthora zeae and
Sclerophthora cryophila, should be included in subsequent
studies. Considering the oen nonspecic and minor symptoms
caused by the phytophthora/sclerophthora-like species aecng
Poales, it seems likely that the few scaered reports of these
organisms are only the p of iceberg of their total diversity.
ACKNOWLEDGEMENTS
Dedicated to the memory of Gary L. Peterson (1964–2022), who
researched Peronosclerospora philippinensis and taught us all.
The authors acknowledge and thank W. Cavan Allen for his
nomenclatural review of this manuscript. We thank John Hall (BPI),
Genevieve Tocci (FH), and Shannon Asencio and Jennifer Wilkinson
(DAOM) for providing specimen imaging, and Yazmín Rivera and Gary
Peterson for sharing images from their collecons. Specimen images
from herbarium BPI prepared for this paper were used by permission of
the USA Naonal Fungus Collecons, USDA-ARS. Specimen images from
DAOM were provided by the Canadian Naonal Mycological Herbarium
(DAOM), ©Her Majesty, The Queen in Right of Canada, as represented
by the Minister of Agriculture and Agri-Food, licensed under the Open
Government License – Canada. We are grateful for the eorts of several
individuals that assisted in the locaon of specimens: Shay Covo and
Dagan Sade (HUJ), Lisa Castlebury and Shannon Dominick (BPI), Maria
Gomzhina (LEP), Dale A. Kruse (TAES/TAMU), Chrisan Scheuer (GZU),
Rossella Marcucci (PAD), Jordan Bailey (DAR), and Genevieve Tocci
and Hannah Merchant (FH). We appreciate Katrien M. Devos at the
University of Georgia for sharing her knowledge about the occurrence
of Sclerospora graminicola in the USA; Gary Peterson and Mo Bonde
of the USDA-ARS for claricaon of Peronosclerospora philippinensis
specimens; and Sujay Rackshit at the Indian Instute of Maize Research
and B.M. Prasanna at CIMMYT for updates on the status of brown stripe
downy mildew disease in India.
This research was supported in part by the appointments of William
J. Davis and Vanina L. Castroagudín to the ARS Research Parcipaon
Program administered by the Oak Ridge Instute for Science and
Educaon (ORISE) through an interagency agreement between the
US Department of Energy (DOE) and USDA. ORISE is managed by
ORAU under DOE contract number DE579AC05-06OR23100. The
ndings and conclusions in this are those of the author(s) and should
not be construed to represent any ocial USDA or USA Government
determinaon or policy. Menon of trade names or commercial
products in this publicaon is solely for the purpose of providing specic
informaon and does not imply recommendaon or endorsement by
the USA Department of Agriculture. The USDA is an equal opportunity
provider and employer.
Funding: This work was funded by USA Department of Agriculture,
Agricultural Research Service projects 8042-22000-298-00-D, 8044-
22000-045-00-D, and by funds to JAC from the Naonal Plant Diseases
Recovery System project 0500-00082-001-00-D and the USDA-APHIS
Plant Protecon Act Secon 7721 program. MT is supported by the
LOEWE iniave of the government of Hessen in the framework of the
Center for Translaonal Biodiversity Genomics (TBG).
Conict of interest: The authors declare that there is no conict
of interest.
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Prof. dr P.W. Crous,Westerdijk Fungal BiodiversityInstitute, P.O. Box 85167, 3508 AD Utrecht, The Netherlands.
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Prof. dr P.W. Crous,Westerdijk Fungal BiodiversityInstitute, P.O. Box 85167, 3508 AD Utrecht, The Netherlands.
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Supplementary Material: hp://fuse-journal.org/
Fig. S1. Eraphthora butleri lectotype BPI 187075.
Fig. S2. Graminivora graminicola lectotype BPI 786232.
Fig. S3. Peronosclerospora maydis isotype BPI 789413.
Fig. S4. Peronosclerospora miscanthi neotype BPI 187301.
Fig. S5. Peronosclerospora noblei lectotype BPI 187306.
Fig. S6. Peronosclerospora philippinensis lectotype BPI 18731.
Fig. S7. Peronosclerospora philippinensis isotype BPI 187044.
Fig. S8. Peronosclerospora philippinensis isotype BPI 187311.
Fig. S9. Peronosclerospora philippinensis isotype BPI 187313.
Fig. S10. Peronosclerospora sacchari lectotype BPI 187331.
Fig. S11. Peronosclerospora sorghi lectotype BPI 187336.
Fig. S12. Peronosclerospora spontanea lectotype BPI 187043
Fig. S13. Peronosclerospora spontanea isotype BPI 187073.
Fig. S14. Peronosclerospora spontanea BPI 187342.
Fig. S15. Sclerophthora cryophila holotype DAOM 20643.
Fig. S16. Sclerophthora macrospora neotype BPI 187265.
Fig. S17. Sclerophthora macrospora isotype BPI 187266.
Fig. S18. Sclerospora farlowii lectotype BPI 187077.
Fig. S19. Sclerospora farlowii isotype BPI 187076.
Fig. S20. Sclerospora farlowii isotype BPI 187078.
Fig. S21. Sclerospora iseilemas lectotype BPI 187262.
Fig. S22. Sclerospora northii lectotype BPI 187307.
Fig. S23. Viennoa oplismeni isotype BPI 784624.
Table S1. Summary of the primary features of the asexual and sexual
structures produced by Peronosporaceae species that cause downy
mildew diseases of Poaceae hosts.

Fig. S1
Eraphthora butleri (W. Weston) Telle & Thines
Lectotype, BPI 187075.
1 cm
Supp. Fig. 1, Crouch et al. 2022
Images courtesy of the United States National Fungus Collections.
Fig. S1. Eraphthora butleri lectotype BPI 187075.

Fig. S2
Graminivora graminicola (Naumov) Thines & Göker
Lectotype, BPI 786232. Supp. Fig. 2, Crouch et al. 2022
Image courtesy of the United States National Fungus Collections.
Fig. S2. Graminivora graminicola lectotype BPI 786232.

Fig. S3
Peronosclerospora maydis (Racib.) C. G. Shaw
Isotype, BPI 789413.
1 cm
1 cm
Supp. Fig. 3, Crouch et al. 2022
Images courtesy of the United States National Fungus Collections.
Fig. S3. Peronosclerospora maydis isotype BPI 789413.

Fig. S4
Peronosclerospora miscanthi (T. Miyake) C. G. Shaw
Neotype, BPI 187301.
Supp. Fig. 4, Crouch et al. 2022
Images courtesy of the United States National Fungus Collections.
1 cm
Fig. S4. Peronosclerospora miscanthi neotype BPI 187301.

Fig. S5
Peronosclerospora noblei (W. Weston) C.G. Shaw
Lectotype, BPI 187306. Supp. Fig. 5, Crouch et al. 2022
Images courtesy of the United States National Fungus Collections.
1 cm
Fig. S5. Peronosclerospora noblei lectotype BPI 187306.

Fig. S6
Peronosclerospora philippinensis (W. Weston) C.G. Shaw
Lectotype, BPI 187314.
3 cm
Supp. Fig. 6, Crouch et al. 2022
Images courtesy of the United States National Fungus Collections.
Fig. S6. Peronosclerospora philippinensis lectotype BPI 18731.

Fig. S7
Peronosclerospora philippinensis (W. Weston) C.G. Shaw
Isotype, BPI 187044.
(G)
(H) (I)
Unless noted, images are courtesy of the United States
National Fungus Collections. Images labeled YR provided
courtesy of Yazm ín Rivera, USDA-APHIS.
Scale bar= 1 cm.
YR
YR
YR
YR
Supp. Fig. 7, Crouch et al. 2022
Fig. S7. Peronosclerospora philippinensis isotype BPI 187044.

Fig. S8
Peronosclerospora philippinensis (W. Weston) C.G. Shaw
Isotype, BPI 187311.
(G)(F)
(H) (I)
1 cm
Supp. Fig. 8, Crouch et al. 2022
Images courtesy of the United States National Fungus Collections.
Fig. S8. Peronosclerospora philippinensis isotype BPI 187311.
e “Supp. Fig. 1 Crouch et al. 2021” to:
t al. 2022” and resend picture.

Fig. S9
Peronosclerospora philippinensis (W. Weston) C.G. Shaw
Isotype, BPI 187313.
(G)(F)
(H) (I)
1 cm
Supp. Fig. 9, Crouch et al. 2022
Images courtesy of the United States National Fungus Collections.
Fig, S9. Peronosclerospora philippinensis isotype BPI 187313.
“

Fig. S10
Peronosclerospora sacchari (T. Miyake) Shirai & Hara
Lectotype, BPI 187331.
1 cm
Supp. Fig. 10, Crouch et al. 2022
Images courtesy of the United States National Fungus Collections.
Fig. S10. Peronosclerospora sacchari lectotype BPI 187331.

Fig. S11
Peronosclerospora sorghi (W. Weston & Uppal) C.G. Shaw
Lectotype, BPI 187336. Supp. Fig. 11 Crouch et al. 2022
Images courtesy of the United States National Fungus Collections.
1 cm
Fig. S11. Peronosclerospora sorghi lectotype BPI 187336.

Fig. S12
Peronosclerospora spontanea (W. Weston) C.G. Shaw
Lectotype, BPI 187043. Supp. Fig. 12 Crouch et al. 2022
Images courtesy of the United States National Fungus Collections.
1 cm
Fig. S12. Peronosclerospora spontanea lectotype BPI 187043.

Fig. S13
Peronosclerospora spontanea (W. Weston) C.G. Shaw
Isotype, BPI 187073. Supp. Fig. 13 Crouch et al. 2022
Images courtesy of the United States National Fungus Collections.
Fig. S13. Peronosclerospora spontanea isotype BPI 187073.

Fig. S14
Peronosclerospora spontanea (W. Weston) C.G. Shaw
Topotype, BPI 187047. Supp. Fig. 14 Crouch et al. 2022
Images courtesy of the United States National Fungus Collections.
1 cm
Fig. S14. Peronosclerospora spontanea BPI 187342.

Fig. S15
Sclerophthora cryophila W. Jones
Holotype, DAOM 20643
(G)(F)
(H) (I)
Supp. Fig. 15 Crouch et al. 2022
Image provided by the Canadian National Mycological Herbarium (DAOM), ©Her Majesty The Queen in Right of Canada,
as represented by the Minister of Agriculture and Agri-Food, licensed under the Open Government License –Canada
1 cm
Fig. S15. Sclerophthora cryophila holotype DAOM 20643.

Fig. S16
Sclerophthora macrospora (Sacc.) Thirum., C.G. Shaw & Naras.
Neotype, BPI 187265
(G)(F)
(H) (I)
Supp. Fig. 16 Crouch et al. 2022
Images courtesy of the United States National Fungus Collections.
1 cm
Fig. S16. Sclerophthora macrospora neotype BPI 187265.

Fig. S17
Sclerophthora macrospora (Sacc.) Thirum., C.G. Shaw & Naras.
Isototype, BPI 187266 Supp. Fig. 17 Crouch et al. 2022
Images courtesy of the United States National Fungus Collections.
1 cm
Fig. S17. Sclerophthora macrospora isotype BPI 187266.

Fig. S18
Sclerospora farlowii Griffiths
Lectotype, BPI 187077
(I)
Supp. Fig. 18 Crouch et al. 2022
Images courtesy of the United States National Fungus Collections. 1 cm
Fig. S18. Sclerospora farlowii lectotype BPI 187077.

Fig. S19
Sclerospora farlowii Griffiths
Isotype, BPI 187076
(H) (I)
Supp. Fig. 19 Crouch et al. 2022
Images courtesy of the United States National Fungus Collections.
1 cm
Fig. S19. Sclerospora farlowii isotype BPI 187076.

Fig. S20
Sclerospora farlowii Griffiths
Isotype, BPI 187078
(H) (I)
Supp. Fig. 20 Crouch et al. 2022
Images courtesy of the United States National Fungus Collections.
1 cm
Fig. S20. Sclerospora farlowii isotype BPI 187078.

Fig. S21
Sclerospora iseilematis Thirum. & Naras.
Lectotype, BPI 187262
(H) (I)
Supp. Fig. 21 Crouch et al. 2022
Images courtesy of the United States
National Fungus Collections.
1 cm
Fig. S21. Sclerospora iseilemas lectotype BPI 187262.

Fig. S22
Sclerospora northii W. We ston
Lectotype, BPI 187307 Supp. Fig. 22 Crouch et al. 2022
Images courtesy of the United States National Fungus Collections.
1 cm
Fig. S22. Sclerospora northii lectotype BPI 187307.

Fig. S23
Viennotia oplismeni Göker, Voglmayr, Riethm., M. Weiß, & Oberwinkler
ex J. A. Crouch & Thines
Isotype, BPI 784624 Supp. Fig. 23 Crouch et al. 2022
Images courtesy of the United States National Fungus Collections.
Fig. S23. Viennoa oplismeni isotype BPI 784624.

Table S1
Supplementary Table S1. Summary of the primary features of the asexual and sexual structures produced by Peronosporaceae species that cause downy mildew diseases of Poaceae hosts. For the complete
descripons, refer to main document text or supplementary materials. Type hosts are highlighted in bold.
Species Hosts Conidiophores/Sporangiophores Conidia/ Sporangia Oogonia Oospores
Baobabopsis donbarrei Peros rara
Cylindrical, evanescent Broadly ellipsoidal, narrowed
slightly approaching base Subglobose Globose to broadly ellipsoidal
Hyaline Golden yellow Subhyaline to golden yellow
75–120 × 20–28 μm 16–20 × 11–18 μm. (27–) 32.5–36.0–39.5 (–45) × (25–)
28–31.7–36 (–39) μm
(19–) 22–24.1– 27 (–29) × (18–)
20–22.5–25 (–28) μm
5–20 terminal ampulliform to
lageniform branches with narrow
neck, 7–14 × 3–7 μm.
Wall uneven, densely verrucose
with rounded warts, 3–9 um thick
(including warts).
Wall smooth, 1–3 μm thick.
Baobabopsis enneapogonis Enneapogon avenaceus,
Enneapogon cylindricus Not observed. Not observed.
Subglobose Globose to broadly ellipsoidal
Golden yellow Pale to golden yellow
(30–) 32.5–36.3–40 (–42) × (29–)
30–33.1–36 (–3 μm 9)
(20–) 21.3–23.0–24.7 (–26) × (19–)
20.5–21.9– 23.5 (–24) μm
Wall moderately verrucose, rounded
warts
Wall (1–) 1.5 (–2) μm thick, even,
smooth.
Uneven, 3–11 μm thick (including
warts)
Remnants of antheridium oen
aached.
Baobabopsis marneyi
Enneapogon polyphyllus,
Enneapogon avenaceous,
Enneapogon cylindricus.
Not observed. Not observed.
Sub-globose to globose Globose to sub-globose
Golden brown Hyaline
(24–) 26–33 (–35) μm diameter (19–) 21–24 (–25) μm diameter
Wall uneven, tuberculate, 3–8 μm
thick (including warts) Adnate (adherent) with oogonial wall
Warts rounded, 3–5 × 2–3 μm. Wall 1–2 μm thick, even, smooth.
Eraphthora butleri
Eragross amabilis,
Eragross aspera,
Eragross cilianensis,
Eragross tremula
Not observed. Not observed.
Spherical to irregularly subspherical Spherical
Pallid golden to dark amber or resin Hyaline
33–36.9 μm (up to 29–40.9 μm)
diameter 19–22.9 μm diameter
Wall relavely even, numerous
bluntly rounded, papillate to nger-
like protrusions, 4–10 μm (excluding
protrusions), protrusions hyaline, base
2–4 μm × 2–5 μm high.
Wall 2–3 μm thick.

Supplementary Table S1. (Connued).
Species Hosts Conidiophores/Sporangiophores Conidia/ Sporangia Oogonia Oospores
Eraphthora drenthii Eragross cilianensis Not observed Not observed
Globose to sub-globose Globose to sub-globose
Light golden (52–) 56–67 (–73) μm diameter
(64–) 68–84 (–92) μm diameter
Adnate (adherent) with oogonial
wall, oen with a single
central vacuole
Wall with straight to
curved, sub-hyaline, digitate
projections 4–7 × 2–3 μm,
uneven, 7–8 μm thick
Wall 6–8 μm thick, even, smooth
Eraphthora occultata Eragross cilianensis Not observed Not observed
Globose to sub-globose Globose to sub-globose
Light golden (57–) 60–71 (–75) μm diameter
(65–) 71–90 (–95) μm diameter
Adnate (adherent) with oogonial
wall, oen with a single
central vacuole
Wall with straight to curved, sub-
hyaline, digitate projections 4–7 ×
3 μm, uneven, 4–10 μm thick
Wall 5–6 μm thick, even, smooth
Graminivora graminicola Arthraxon hispidus
Curved, hyaline Globose to ovoid
Not observed Not observed
Up to 600 μm long × 9–10 μm wide
at base, with inated base above
stomata, 5–6 μm wide at terminal
ramicaons
Hyaline
Dichotomous or irregular branching
in the upper part (4–6 branches)
Short basal and papilla at the
slightly aened apical end
Terminal inated vesicle carrying four
sterigmata (somemes two, up to
eight, typically in even numbers)
Mode of germination
not observed
Peronosclerospora arisdae Aristida hygrometrica Not observed Not observed
Globose to sub-globose Globose to sub-globose
Golden yellow Golden yellow
(30–) 39–51 (–53) μm diameter (23–) 27–31 (–32) μm diameter
Wall 6–14 μm thick, with sparse, low,
irregular, truncate ridges
Fused with oogonium wall
Wall hyaline, 1–2 μm thick, even,
smooth
Peronosclerospora boughtoniae Sorghum plumosum Not observed Not observed
Globose to sub-globose Globose
Light golden brown Hyaline
(25–) 29–40 (–50) μm diameter (22–) 24–29 (–31) μm diameter
Wall smooth occasionally scabrid,
aened sides bordered by
inconspicuous ridges, 1–12 μm thick
Wall 1–2 μm thick, even, smooth
Table S1 (Connued).

Supplementary Table S1. (Connued).
Species Hosts Conidiophores/Sporangiophores Conidia/ Sporangia Oogonia Oospores
Peronosclerospora
dichanthiicola Dichanthium annulatum
Globose to obovoid
Not observed Not observed
Hyaline
Thin-walled
21–28 × 15–18 μm
Evanescent, nocturnal, erect
83–130 μm long × 13 μm wide at
basal cell septum, 17–27 μm wide at
branching point
Basal cell isodiametric, 33 μm × 13
μm, discreet knob-like structure at
base
Dichotomously branched, (rare
secondary and terary branching),
2–6 in number, 33–37 μm × 83–90
μm wide
Primary branches with 2–3 obconical
tapering sterigmata with conidia
Germination by germ tubes
Peronosclerospora eriochloae Eriochloa
pseudoacrotricha
Globose to subglobose Globose to subglobose Globose
Hyaline Orange to luteus Hyaline
(9–) 13.3 (–18) × (9–) 12 (–13.4)
μm (33–) 46.6 (–70) µm diameter (27–) 33.5 (–46) μm diameter
No operculum, no pore;
germination by one or two
germ tubes
Wall hyaline, confluent with
oospore wall, 1.0–1.5 μm thick
Wall in two layers: exosporium
reddish brown, 2–15 μm thick;
endosporium hyaline, 2–3 μm thick
Evanescent, nocturnal, erect
Hyaline
245–280 μm long with swollen
base 6–13 μm wide, 6–9 μm wide
at septum, 20–30 μm wide above
septum and at the start of branching;
septum 90–115 μm above base
Dichotomously branched with
secondary, terary and quaternary
branches, 45–100 μm wide
Sterigmata at branch tip, conoid-
subulate 4–9 × 3–4 μm
Peronosclerospora
heteropogonis
Heteropogon contortus,
Zea mays
Globose
Not described
Globose, tuberculate
Hyaline
14.3–22.4 × 14.3–20.4 (17.7 ×
16.2) μm (24.5–) 29.0 (–36.7) μm diameter
Evanescent, nocturnal
Hyaline
81.6–142.8 × 14.3–255.5 μm from
base to branching (average: 101.8 ×
20.1 μm) with erect, swollen base.
Dichotomously branching with
secondary and tertiary branches
Mostly fused to oogonial wall
Thin-walled, no operculum, no
pore
Germination by germ tubes Germination by zoospores
Table S1 (Connued).

Supplementary Table S1. (Connued).
Species Hosts Conidiophores/Sporangiophores Conidia/ Sporangia Oogonia Oospores
Peronosclerospora ischaemi Ischaemum fragile Not observed Not observed
Globose
(35 −) 41−48 (−50) μm diameter
Subglobose to irregular
Golden brown
(55−) 61−68 (−70) × (49−) 56−65
(−68) μm
Wall 5−20 μm thick,
uneven, flattened, smooth
Adnate (adherent) with oogonium
wall, with a single vacuole
Wall hyaline, 4−6 μm thick,
even, smooth
Peronosclerospora jamesiae Sorghum intrans Not observed Not observed
Sub-globose to ovoid somemes
with a aened side, with a
prominent oil globule
(30–) 32–42 (–55) μm diameter
Shape highly variable including sub-
globose, ovoid and cuboid
Dark golden brown
(40–) 46–60 (–80) μm diameter
Wall smooth, rounded to flat,
occasionally concave, 2–15 μm thick
Wall 1–2 μm thick, hyaline,
even, smooth
Peronosclerospora mactaggari Sorghum morense Not observed Not observed
Sub-globose to globose Globose
Light golden brown
(30–) 33–36 (–40) μm diameter (23–)25–27(–29) μm diameter
Wall smooth, uneven, 1–8 μm thick. Adnate with oogonial wall, with a
single vacuole
Wall 1–2 μm thick, hyaline, even,
smooth
Peronosclerospora maydis
Euchlaena mexicana,
Saccharum spontaneum,
Zea mays
Robust, erect Oval or spherical to subspherical,
non-papillated
Globose, subglobose, broadly
ellipsoidal to irregularly
polyangular
Golden orange to yellowish
or reddish brown
55–76 μm diam
Wall 2–15 μm wide, uneven,
smooth, convoluted
Subglobose or broadly ellipsoidal
Sub-hyaline to pale yellow
39–55 μm diam
Often with a large vacuole
Wall 2.5–4.0 μm wide, even, smooth
One per oogonium
Hyaline
Robust, erect, 200–550 µm long ×
20–25 mm thick 15–18 mm wide
Dichotomously branched 2–4
mes; branchlets with 2–6 conical
sterigmata (6–9 mm long)
One sporangium per sterigmata.
Basal cells septate, 60–180 µm long Germination by 1–2 germ tubes
Peronosclerospora miscanthi
Miscanthus japonicus,
Miscanthus sinensis,
Saccharum ocinale,
Saccharum robustum,
Saccharum spontaneum
Elongately ovoid Reddish brown
43.5–47.1 μm diameter
(37.2–) 41.8 (–48.6) × (14.3–) 18
(–22.9) μm (average 41.8 × 18)
μm
58.3–63.5 × 51.5–56.9 (range=43.2–80
× 33.2–64.8) μm
97–300 (up to 438) μm long × 12–37
μm wide
Branched twice at the tip, with >20
conidia per tip Germination by germ tube Walls unevenly thick, 3–8 μm to 12–
24 μm thick, with small excrescences
Table S1 (Connued).

Supplementary Table S1. (Connued).
Species Hosts Conidiophores/Sporangiophores Conidia/ Sporangia Oogonia Oospores
Peronosclerospora noblei
Sarga leiocladium,
Sorghum leiocladum,
Sorghum plumosum
Not observed Not observed
Ovoid, ellipsoid, pyriform or
subspherical; overall shape gibbous
and unsymmetrical
Spherical, hyaline to pale golden
28–44 μm (20–) 23–28.9 (–34) μm in diameter
Wall of variable thickness: (3–) 5–10
(20) μm think, giving appearance of
bluntly rounded projecon
Wall 1–1.5 μm thick
Wall golden to rich brown Granular contents, dense
aggregaons and oil drops
Oogonial stalk fragments retained. Germinaon not observed.
Peronosclerospora panici Panicum laevinode Not described Not observed Not observed
Globose to sub-globose, rarely
ovoid
Hyaline, aseptate
(15–) 15–17 (–20) × (12–
) 13– 16 (–18) μm
Wall thin, without operculum or
pore
Germination by germ tube
Peronosclerospora philippinensisZea mays, 18 other
Poaceae hosts
Evanescent, nocturnal, erect
Elongate ellipsoid, elongate
ovoid, or rounded cylindrical,
apex slightly rounded, with a
minute apiculus at the base
22.9 μm diam
Wall smooth
Fragments of oogonial
stalk or antheridia often
adherent
Spherical
Hyaline or straw-colored
(15.3–)19.2(–22.6) μm diam
Wall smooth, 2.0–3.9 μm thick
Contents finely granular with oil
droplets
Positioned central to eccentric
Germination via one germ tube
Hyaline
150–400 × 15–26 μm with basal cell,
dichotomously branched two to four
mes
Sterigmata conoid to subulate and
slightly curved, 10 μm long. 17–21 × 17–39 μm
Episporium thin
Minutely granular contents;
germination by germ tube
Peronosclerospora sacchari Saccharum ocinarum,
Zea mays, Zea mexicana
Sporangia ellipcal or oblong Irregularly ellipcal Globular
Hyaline Castanian brown Yellow
25–41 × 15–23 μm, or 49–54 ×
19–23 49–58 × 55–73 μm 40–50 μm diameter
Fugacious, erect
Hyaline
160–170 μm long × 10–15 μm wide
at base but middle secon wider,
branched 2–3 mes, each branch
stocky, conical shaped.
Wall smooth, thin
Wall thickness unequal Wall 3.8–5 μm thick
Apex rounded, base slightly
apiculate or rounded
Wall thin and smooth;
germination by germ tubes Germination by germ tubes
Table S1 (Connued).

Supplementary Table S1. (Connued).
Species Hosts Conidiophores/Sporangiophores Conidia/ Sporangia Oogonia Oospores
Peronosclerospora sargae Sorghum morense Not observed Not observed
Globose, subglobose to broadly
ellipsoidal, occasionally irregularly
polyangular
Globose
Pale yellow to yellowish brown Pale yellow
(30–) 37.9 (–47) μm diameter (24–) 29.3 (–34) μm diameter
Wall 2–8 μm smooth, wide, uneven
Oen containing large vacuole
Wall (1.5–) 2.1 (–3.0) μm wide,
even, smooth
Peronosclerospora schizachyrii Schizachyrium fragile Not observed Not observed
Globose to sub-globose Globose to sub-globose
Hyaline
(26–) 29–39 (–47) μm diameter
Golden brown
(35–) 41–55 (–65) μm diameter
Wall uneven, 6–32 μm thick,
polyangular, smooth
Adnate with oogonial wall; contains a
single vacuole
Wall 1–4 μm thick, even, smooth
Peronosclerospora sehimas Sehima nervosum Not observed Not observed
Globose to sub-globose Globose
light golden brown (28–) 34–42 (–46) μm in diameter
(38–) 45–58 (–63) μm diameter Adnate with oogonial wall; contains a
single vacuole
Wall smooth, uneven, 3–15 μm thick Wall 2–4 μm thick, hyaline, even,
smooth
Peronosclerospora sorghi
Panicum maximum,
Roobellia exalta,
Sorghum bicolor,
Sorghum spp., Zea mays,
Zea mexicana
Erect, spreading, comprising basal
cell, main axis and more or less
complex
Suborbicular Thick Spherical
Hyaline Irregularly polygonally-angled
oogonial wall closely enveloping
the oospore
Hyaline
100–150 μm length to the septum;
main axis 15–25 μm diameter; basal
cell 7–9 μm, knobbed or bulbous at
base
21–24.9 × 19–22.9 (range 15–
28.9 × 15–26.9) μm
31–36.9 (mode 35–36.9 μm, range
25–42.9) μm diameter
Usually dichotomously branched;
branching in short, stout dichotomies
with primary, secondary, and terary
branching
Wall thin
Wall light Mars Yellow, 1.1–2.7 (range
0.3–4.3 μm ) μm thick
Branches terminating in
tapering sterigmata, 13 μm long
Germination by germ tubes Finely granular contents, oil globules
Germinaon by branched, hyaline
germ tube, 4.4 μm average width
(range 2.5–8.3 μm)
Table S1 (Connued).

Supplementary Table S1. (Connued).
Species Hosts Conidiophores/Sporangiophores Conidia/ Sporangia Oogonia Oospores
Peronosclerospora spontanea
Miscanthus japonicus,
Saccharum spontaneum,
Saccharum ocinarum,
Zea mays, Zea mexicana
Evanescent, nocturnal, erect, single
or grouped Elongately ellipsoid or cylindrical
Not observed Not observed
Hyaline
350–550 μm length, basal cell 140–
260 × 5–8 μm 39–45 × 15–17 μm
Complex dichotomous branching Finely granular content, thin
walled
Straight terminal sterigmata, 13
μm long
Rounded apex lacking papilla,
rounded base with apiculum of
aachment
Germination by germ tubes
Peronosclerospora westonii Iseilema prostratum
Globose to ovoid Spherical, subglobose Spherical
600–1000 long × 9–11.5 μm broad
at the basal cell, 20–27 μm broad at
main axis branching.
Hyaline Golden-brown
Dichotomous branches 20–25 ×
12–15 μm; typically limited to 2–4
primary branches with 2–3
obconical tapering sterigmata.
12–19 μm diameter 40–50 μm diameter 23–29 μm diameter
Granular contents at maturity,
thin walled Granular contents Wall 6–9 μm thick; covered by
the outer oogonial wall layer
Germination by germ tubes
Poakatesthia pennise Pennisetum glaucum
Amphigenous, erect Wide obovoid, with aened
apical end
Not observed Not observed
Hyaline Hyaline
300–580 μm high; trunk 0.55–0.77 of
total height × 8–11 μm width 19–23.7 × 14.2–17 (19) μm.
Dichotomously branched once or
twice, then branched irregularly
monopodially to subdichotomously
two or three times at right angles
Poroid papilla; base peducellate
Sclerophthora cryophila
Dactylis glomerata,
Apluda muca,
Dichanthium annulatum,
Digitaria marginata,
Heteropogon contortus
Nocturnal under natural condions. Obpyriform, hyaline Subglobose to spherical, sinuous Spherical
Short, sterigma-like (22.5–) 30.5–38 (–45.5) × (11.5–)
15–19 (–22.5) μm Golden to amber-brown (20–) 31.8 (–37.5) μm diameter
Unbranched
Poroid apex (29.5–) 38.5 (–51.5) μm diameter Wall (1.5–) 2.6 (–3.5) μm
thick; confluent with oogonial
wall
Persistent pedicels
Wall (1.9–) 3.7 (– 3.8) μm thick
(average 3.7)
Antheridia paragynous
Table S1 (Connued).

Supplementary Table S1. (Connued).
Species Hosts Conidiophores/Sporangiophores Conidia/ Sporangia Oogonia Oospores
Sclerophthora lolii Lolium rigidum Short, thin Lemon-shaped, thin walled Spherical to subspherical, sinuous Spherical
Hyaline
25.2–28.8 μm diameter Golden brown
Thick walled 10.8–18.0 μm diameter
(40.7–) 55.0 (–63.7) × 25.2–35.0
μm
Base with persistent peduncle,
apex papillate, poroid, thin
walled
Germinaon by pyriform
zoospores, 7.8–10.7 μm long,
escape via sporangial apex
Smooth-walled, moderately thin
walled, ventrally located within
confluent oogonial walls
Sclerophthora macrospora Phlaris arundinacea, plus
37 other Poaceae hosts
Sympodial
Limoniform, obovate or
ellipsoidal, moderately papillate,
hyaline to slightly purplish
Globose Globose, aached closely to the wall
of the oogonium
(8–) 14 (–28) mm long, 1–4 mm wide
58–98 × 30–65 mm (natural
material) or (65–) 87 (–113) ×
(33–) 44 (–55) mm (in water).
Light greenish to greenish brown Hyaline
Undifferentiated from hyphae
Germinaon by ovate or
irregularly kidney shaped
zoospores (13–) 11(–16) ×
(10–) 13 (–14) µm; may produce
zoosporangia (10–) 13 (–16)
with germ tubes 1.6–2.5 mm
wide
50–95 × 55–100 mm (mostly 57–73 ×
63–75 mm) (43–) 57 (–70) × (43–) 60 (–73) mm
Wall 2.5–7.5 mm thick Wall (3.8–) 6.5 (–10) mm thick
Antheridia laterally aached, hyaline
to light yellow, obovate to ellipsoidal
[(13–) 15 (–23) × (23–) 28 (–41) mm],
wall slightly thick [(1.8–) 2.5 (–3.8)
mm]
Germination by germ tube
Sclerophthora rayssiae Hordeum vulgare
Very short, hyphal Lemon shaped or ovate, never
obpyriform, hyaline Usually sinuous, unevenly thickened Globular, occasionally subglobular
Nocturnal
44.4–59.2 (61.4) μm Light golden amber
Antheridia paragynous, closely
appressed to oogonium
(29.6–) 33.3 (–44.4) μm
28.8–55.0 × 19.2–27.9 μm
Base with wedge-shaped pedicel,
apex poroid and protruding,
granular
Germinaon by reniform,
biflagellate zoospores, 7.5–11.0
μm
Wall deep golden brown, smooth
and thin
Usually eccentrically located within
oogonial wall
Table S1 (Connued).

Supplementary Table S1. (Connued).
Species Hosts Conidiophores/Sporangiophores Conidia/ Sporangia Oogonia Oospores
Sclerophthora zeae
Digitaria bicornis,
Digitaria sanguinalis, Zea
mays
Short, hyphal
Subglobose Spherical or subspherical
Hyaline to light straw-colored Hyaline
33–44.5 μm diameter 29.5–37.0 μm diameter
Thin-walled Wall smooth and glistening, 4 μm
thick, conuent with oogonial wall
Ovate, obclavate, or ellipc or
cylindrical
Hyaline
29.0–66.5 × 18.5–26.0 μm,
poroid apex truncate or rounded,
with a persistent, straight or
curvate peduncle
Smooth-walled
Germinaon by 4–8 spherical
hyaline zoospores, 7.5–11.0 μm
diameter
With 1– 2 paragynous antheridia. Oil globule, centrally located
Sclerospora farlowii Chloris virgata Not observed Not observed Not described
Subglobose
Deep dark reddish brown and oen
appearing black and opaque
28–45 μm diameter
Sclerospora graminicola
Setaria viridis,
Pennisetum glaucum; 20
species of Poaceae from
13 genera
Ellipcal, slightly pointed at the
free end Ellipcal, angular or irregular shape Spherical
Hyaline Tawny to brown or chestnut brown Yellow (Chromotaxia)
Evanescent, nocturnal, erect
100 µm × 12–15 µm
Branches in the lower part; branches
thick, dichotomous or trichotomous
branching at the top, crowned with
numerous papillae where sporangia
form
(34—) 42 (–52) μm diameter (22.5–) 32 (–35) μm diameterThin smooth wall
Germinaon by irregularly kidney
shaped, unequal-sided, aened
zoospores, 9–12 μm, with two
cilia on the concave side
Wall irregular, thickened areas, with
conspicuous ridges, 4 1 mm thick,
sometimes up to 17 mm
Wall evenly thickened, smooth
Sclerospora iseilemas Iseilema prostratum Not observed Not observed
Subglobose to spherical Spherical
Pale golden-yellow Hyaline
43–61 mm 38–50 mm
Wall deeply folded, tuberculate,
almost spiny Pleroc
Wall 5.5 mm thick Inner granular contents, a few
droplets enclosed.
Antheridia 2–5, conoid to triangular,
27–40 × 15.5–27 mm, persistent in
mature oospore
Wall 3–3.5 mm thick, confluent
with the oogonial wall
Table S1 (Connued).

Supplementary Table S1. (Connued).
Species Hosts Conidiophores/Sporangiophores Conidia/ Sporangia Oogonia Oospores
Sclerospora northii Saccharum maximum Not observed Not observed
Rounded polyhedral, several aened
faces bordered by ridges, occasionally
irregular, elongate pyriform, or
unequally rounded oblong
Spherical, hyaline to pale amber
Amber Brown (somemes Raw
Sienna, to Argus Brown)
39–46.9 mm (mode 41–44.9 mm; up
to 35–52 mm)
40–70 mm (up to 57–60.9 mm length
× 51–56.9 mm width)
Finely granular contents, typically
with oil globules at the center
Wall 3–5 (up to 10) mm thick, with
arched irregular, ridged prominences Wall dense, smooth, homogeneous
to indisnctly lamellate, 2–4.5 mm
thick
Remains of oogonial stalk
or antheridium rare
Sclerospora secalina Secale cereale Not observed Not observed
Sub-spherical, 33–38 (or 48) mm
diameter Spherical, deep ocher, then brown
Antheridia 14.7 × 18 mm diameter 31–46 (or 36) mm diameter at
maturity
Wall smooth without tubercules
or ridges Wall smooth
Viennoa oplismeni Oplismeni compositus Not observed Not observed
14–28 × 11–17 mm
Hyaline
180–230 mm × 6–8 mm
Monopodial branching, spreading
branching in the upper third secon
Terminal branches straight to slightly
curved with short right-angled
ramicaons, terminal swellings with
three sterigmata
Sterigmata bloated and pinched, 14–
23 mm length
Table S1 (Connued).