Exosporium gymnemae sp. nov. from India

Abstract

A new species, Exosporium gymnemae is proposed as a saprobe associated with dead stems of Gymnema sylvestre. It has distinct morphological characters, especially the conidiophores which form large, compact, blackish brown synnemata with glazed surface and cylindrical to obclavate conidia with dark bands at the septa. A literature-based checklist of Exosporium species together with their respective hosts and geographic locations is also provided.

Full text

Submitted 22 June 2015, Accepted 12 July 2015, Published online 10 September 2015
Corresponding Author: Paras N. Singh – email – pnsingh@aripune.org 508
Exosporium gymnemae sp. nov. from India
Singh PN*, Baghela A, Singh SK and Maurya DK
National Fungal Culture Collection of India, Biodiversity and Palaeobiology Group, Agharkar Research Institute,
Gopal Ganesh Agarkar Road, Pune, India 411004
Singh PN, Baghela A, Singh SK, Maurya DK 2015 – Exosporium gymnemae sp. nov. from India.
Mycosphere 6(5), 508–514, Doi 10.5943/mycosphere/6/5/1
Abstract
A new species, Exosporium gymnemae is proposed as a saprobe associated with dead stems
of Gymnema sylvestre. It has distinct morphological characters, especially the conidiophores which
form large, compact, blackish brown synnemata with glazed surface and cylindrical to obclavate
conidia with dark bands at the septa. A literature-based checklist of Exosporium species together
with their respective hosts and geographic locations is also provided.
Keywords – microfungi – Pezizomycotina – taxonomy – Western Ghats.
Introduction
The Western Ghats comprise mountain ranges in southwestern India that are rich in
evergreen rainforests. They are recognized as biodiversity hotspots by virtue of their rich flora and
fauna, including endemic species. Our studies on fungal diversity have led to the identification of
several novel fungi from this region (Karandikar & Singh 2010, Rajeshkumar et al. 2012,
Senthilarasu & Singh 2013, Sharma & Singh 2013, Singh et al. 2009, 2010, 2012). During
exploration of fungal diversity in the sacred grooves of Mulshi forest of Western Ghats region of
Maharashtra (November 2011), several microfungi were collected for taxonomic study. An
interesting effuse, hairy, compact, and glazed fruiting structure around dead stem of Gymnema
sylvestre was encountered. This taxon turned out to be a compact synnematous species bearing
cylindrical to obclavate conidia with distinct septation pattern and variable in size. Based on its
distinct features, the fungus is described as a new species of Exosporium Link.
Exosporium is a hyphomycetous genus with saprobic (Ellis 1961, Zhao 2012) and
endophytic or phytopathogenic (Ramakrishnan 1957, Braun & Nakashima 2014) life styles, and is
widely distributed. Kirk et al. (2008) considered there to be about 19 valid species of Exosporium
(typified by Exosporium tiliae). Since then, a further five species have been added to the genus,
viz., E. livistonae (Crous & Summerell 2011), E. machili (Zhao & Zhao 2012), E. husanum (Zhao
2012), E. petersii (Braun 2014) and E. miyakei (Braun & Nakashima 2014). Table 1 depicts details
of validly described species, in the genus.
Materials & Methods
Isolates and morphology
After collection from type locality, specimens were brought to the laboratory in separate
paper bags. A trinocular Nikon stereo microscope (Model SMZ-1500 with Digi-CAM, Japan) was
Mycosphere 6 (5): 508–514(2015) ISSN 2077 7019
www.mycosphere.org Article Mycosphere
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Doi 10.5943/mycosphere/6/5/1

509
Fig. 1 – Exosporium gymnemae AMH 9666, A: Synnemata on substrate, B: Enlarged view of erect
synnmeta arising from substrate (dead stem), C–E: Conidia attached to conidiophores, and dark
glazed synnemata. – Bars C=10 µm; D, E=20 µm.
used to study features of the fungus on stem surface and for taking photomicrographs. A scrape was
taken from growing colonies and mounted in lactic acid cotton blue and examined using an AXIO-
10 Carl Ziess microscope. Microphotographs were taken of various morphological structures. The
holotype specimen is deposited in Ajrekar Mycological Herbarium (AMH), MACS’ Agharkar
Research Institute, Pune, India with the accession number AMH 9666. The present taxon was
compared to the closely related synnematous species of Exosporium.
Attempts to culture the species on artificial media, such as potato dextrose agar and potato
carrot agar (Tuite 1969) were unsuccessful.

510
Fig. 2 – Exosporium gymnemae sp. nov. A–B: Polytretic condiogenous cells with prominent
circular scars, C: Conidiophores with terminal conidiogenous cells, D–G: Conidia attached to
conidiophores, H: Echinulate conidium with truncate base. – Bars A–C=10 µm; C=20 µm; D=20
µm; E=10 µm; F, G=20 µm; H=10 µm.
Results
Taxonomic description
Exosporium gymnemae PN Singh, S.K Singh, sp. nov. Figs 1–2
MycoBank MB 812842
Type – on dead stem of Gymnema sylvestre R.Br. (Apocynaceae), Sacred Groove (18° 50' N;
73° 50' E) Mulshi, Distirct Pune, Maharashtra, India, 7 November 2011, coll. P.N. Singh, AMH
9666 (holotype), PNS-ARI 11 (isotype).
Etymology – Latin, gymnemae refers to a generic name of host 'Gymnema '.
Colonies on dead stem punctiform, hairy, brown to black, elongated growing all around the
stem surface. Stromata immersed in the substratum, cells compact, pseudoparanchymatous, dark
brown. Conidiophores arising from cells of stromata, unbranched, flexuous, septate, dark brown to
golden brown, 12.5 µm wide at the widest part, closely adpressed forming synnemata, erect, black,
glazed surface, wider near the base, 2200–3000 × 50–100 µm. Conidiogenous cells integrated,
terminal to lateral or intercalary, sympodial proliferation, smooth-walled, olivaceous brown, rarely
denticulate, cicatrized, scars prominent (up to 14) forming circular ring, up to 6 µm diam., in front
view visible as central pore. Conidia acropleurogenous, solitary, straight to slightly curved, clavato-
cylindric to obclavate, echinulate, thick-walled, pale to dark brown, basal and apical cells
sometimes paler or subhyaline, euseptate (2–15 septa), constricted at septa, septation pattern
variable (sigmoid, lanceolate and flat band like), base truncate with thick, dark brown scar, apex
obtuse to broadly rounded, some conidia with short beak, 21–157 × 16–41.5 µm.

511
Discussion
There are four other species of Exosporium that produce synnemata: E. monanthotaxis
(Pirozynski 1972), E. ramosum (Ellis 1971), E. assamicum (Agnihothrudu 1966) and E. petersii
(Braun 2014). However, E. gymnemae has the largest, glazed, highly compact synnemata, and
widest (16–41.5 µm), clavato-cylindric to obclavate conidia which are rough walled/echinulate and
euseptate. The sigmoid, lanciolate and flat band like septation pattern in new species is also distinct
from other species in the genus. Based on these salient features, this taxon is distinct from others in
the genus.
Exosporium gymnemae is compared with non-synnematous species of Indian origin. It
differs from E. coonoorense (Subramanian 1956) in having shorter and wider conidia. The conidia
of E. gymnemae are significantly longer and wider than those of E. bryophylli (Ramakrishnan
1957), E. fici (Payak & Thirumalachar 1957) and E. ochroleucas (Munjal & Kulshreshtha 1966).
Exosporium lycopersici (Khan & Sullia 1981), another species described earlier from India, needs
to be re-classified as illustrations in the original paper suggest that it is probably a chain forming
species of Corynespora (Table 2).
Table 1 Hosts and distribution of Exosporium species.
Species
Hosts
Country/Region
References
E. acrocomiae
Acrocomia media (leaves)
Puerto Rico
Chupp ex Stevenson
(1975)
E. ampullaceum
Funtumia sp., Rauwolfia sp.,
Theobroma sp. (dead twigs and
branches)
Sri Lanka, Ghana, Sierra
Leone, India
Ellis (1961)
Ex. assamicum
Albizzia chinensis (dead branch)
India (Assam)
Agnihothrudu (1966)
Ex. bryophilli
Bryophillum calycinum (leaves)
India (Kerala)
Ramakrishnan (1957)
Ex. catenulatum
Gymnanthes llucida (dead
twigs)
Cuba
Ellis (1976)
Ex. cinnamomi
Cinnamomum zeylanicum
(leaves)
India (Coorg, Mysore)
Muthappa (1966)
Ex. coonoorense
Eugenia sp. (twigs)
India (Coonoor, Madras)
Subramanian (1956)
Ex. extensum
Erythrina sp. (dead branch)
Sri Lanka
Ellis (1961)
Ex. fici
Ficus benghalensis (leaves)
India (Maharashtra)
Payak & Thirumalachar
(1957)
Ex. husanum
Unidentified (dead twigs)
China (Yunnan)
Zhao (2012)
Ex. indicum
Michelia nilgirica (dead twigs)
India (Madras)
Tilak (1966)
Ex. lavistonae
Lavistona benthami (leaves)
Australia
Crous & Summerell
(2011)
Ex. leptoderridicola
Leptoderris fasciculata (dead
twigs)
Sierra Leone
Ellis (1961)
Ex. lycipersici
Lycopersicon esculentum
(fruits)
India (Bangalore,
Karnataka)
Khan & Sullia (1981)
Ex. machili
Machilus sp. (leaves)
China (Yunnan)
Zhao & Zhao (2012)
Ex. mexicanum
Erythrina sp., Mascagnia,
Smilax, Uveria (dead stems and
branches)
India, Sri Lanka, Mexico,
New Guinea, Philippines,
Sierra Leone, USA
Ellis (1963)
Ex. miyakei
Smilax glauca (leaves)
USA (South Carolina)
Braun & Nakashima
(2014)
Ex. monanthotaxis
Monanthotaxis sp. (dead twigs)
Tanzania, India (Salmalia,),
Puerto Rico, Venezuela
Pirozynski (1972)
Ex. nattrassii
Croton macrostachys (dead
branches)
Kenya
Ellis (1961)
Ex. occidentale
Cornus sp. (dead branches)
Canada (Manitoba,
Saskatchewan)
Sutton (1973)
Ex. ochroleucum
Dead branch
India (Hamirpur, Punjab)
Munjal & Kulshreshta
(1966)

512
Species
Hosts
Country/Region
References
Ex. petersii
Smilax nipponica (leaves)
Japan
Braun (2014)
Ex. pterocarpi
Pterocarpus indicus (leaves)
Malaysia
Ellis (1961)
Ex. ramosum
Pinus sp. (dead needles)
USA
Ellis (1976)
Ex. stilbaceum
Elaes sp. (leaves)
Congo, Ghana,Sudan,
Zambia, Sierra, Leone
Ellis (1961)
Ex. tamarindi
Tamarindus indicus (leaves)
Godavari, Andhra Pradesh,
India
Sydow & Sydow
(1913)
Ex. tiliae
Tilia sp. (branches and twigs)
Europe
Link (1809)
E. wisteriae
Dead branch of Wisteria
sinensis
Romania
Sandu (1968)
Table 2 Comparison of morphotaxonomic features of Exosporium gymnemae sp. nov. with
synnematous, and non synnematous species of Indian origin.
Exosporium spp.
Synnemata
Conidiophores
Conidia
E. assamicum
Up to 1–mm
long, 250 µm
wide.
Fasciculate, unbranched, slightly darker at
the apex, scars conspicuous.
Cylindrical to obclavate, 15–
distoseptate,140–190 × 24–
36 µm.
E. bryophilli
Absent
In cluster, erumpent, unbranched, dark
brown, 140–285 × 4–6 µm. Scars
conspicuous.
Fusiform or clavate, 3
euseptate, 28–25 × 8–10 µm.
E. coonoorense
Absent
In cluster, unbranched, darker at base,
paler above, 770 µm long, 12 µm thick;
scars thickened and darkend.
Obclavate, 10–20 euseptate,
90–200 × 22–33 µm.
E.cinnamomi
Absent
Fasciculate, unbranched, dark brown, 200–
720 × 4.5–5.6 µm. Scars thickened.
Obclavate, 3– distoseptate,
26–60.8 × 8.5–11 µm.
E. fici
Absent
Arising in sprodochia, unbranched,
densely compacted, brownish black, 17–
32 × 5–7 µm.
Obclavate to cylindric, 3–5
euseptate, 23–92 × 3.5–7
µm.
E. indicum
Absent
Fasciculate, brown to dark brown, 180–
260 × 9.3–15 µm. Scars thickened.
Obclavate, 3–8 distoseptate,
90–130 × 9.3–19 µm.
E. lycopersici
Absent
Fasciculate, dark brown, thick walled,
218.5–425.5 × 9–11.5 µm.
Obclavate, fusiform to
cylindric, straight or
variously curved, solitary or
catenate, 2–11 distoseptate,
35–160 × 7.5–17.5 µm.
E. monanthotaxis
1–1.5 mm long
50–150 µm wide
Conidiophores 3–4 µm wide near base, 8–
10 µm wide at apex. Scars prominent.
Obovoid to obclavate, 4–7
distoseptate, 40–70 × 15–
17µm.
E. ochroleucum
Absent
Fasciculate, unbranched, brown to dark
brown, 100–380 × 10–12 µm. Scars
thickened.
Obclavate, 7–10 distoseptate,
36–100 × 8–14 µm.
E. petersii
Present
Loose to dense fasciculate 2–25in group,
coremioid, rarely branched, 30–250 × 3–6
µm. Conidiogenous cells occasionally
percurrent, enteroblastic. Scars slightly
thickened.
Obclavate, alternarioid, with
very long pale beak in some
conidia, small conidia
broadly fusiform, 2-11
distoseptate, 20–130 × 4–8
µm.
E. ramosum
Present
Caespitose, branched towards apex, brown
or dark brown, 400 µm long, 6–9 µm
wide; scars 1–4, conspicuous and dark.
Fusiform to obclavate, 3–5
euseptate, 28–38 × 8–11µm.
E. tamarindi
Absent
Arising in sporodochia, fasciculate,
aseptate, fuliginous, 4–6 µm wide.
Vermiform, obtuse at the
ends, 3–10 euseptate, 18–45
× 4–6.5 µm.
E. gymnemae
2200–3000 ×
50–100µm.
Flexuous, septate, dark brown to golden
brown, 12.5 µm wide at the widest part.
Clavate to obclavate, 2–15
euseptate, 21–157 × 16–
41.5 µm.

513
Acknowledgment
We are grateful to The Director, MACS-Agharkar Research Institute for providing the
necessary facilities to carry out the research.
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