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Plant Pathol. J. 28(4) : 453 (2012)
http://dx.doi.org/10.5423/PPJ.DR.06.2011.0106
pISSN 1598-2254 eISSN 2093-9280
The Plant Pathology Journal
© The Korean Society of Plant Pathology
First Confirmed Report of Powdery Mildew Caused by Erysiphe aquilegiae on
Casuarina cunninghamiana in Argentina
Silvia Wolcan1, Sung-Eun Cho2, Ji-Hyun Park2 and Hyeon-Dong Shin2*
1CIC - Centro de Investigaciones de Fitopatologia, Facultad de Ciencias Agrarias y Forestales, 60 y 119, 1900 La Plata, Argentina
2Division of Environmental Science and Ecological Engineering, Korea University, Seoul 136-701, Korea
(Received on June 4, 2011; Accepted on January 27, 2012)
Casuarina cunninghamiana Miq. (Fam. Casuarinaceae) is native to
Australia and was introduced to Argentina and used as a windbreak,
shade tree and for ornamental purposes. In autumn 2009, the potted
seedlings in the nursery of La Plata University were found to be
infected with a powdery mildew. Symptoms first appeared as thin
white colonies, which subsequently developed into an abundant
growth on the leaves and young stems (Fig. 1A). The damage caused
by the powdery mildew infection has been observed every year after
this initial infection and was again confirmed in April, 2011. There
have been a few reports on the presence of powdery mildew on
Casuarina spp. (Mantz et al., 2008; Farr and Rossman, 2011). In all
the reports, the pathogen was cited to be Oidium sp. Thus, the aim of
this work was to identify the causal agent of the powdery mildew
observed on casuarina in Argentina.
A detailed microscopic examination of a representative sample
(KUS-F24744) deposited in Korea University was made to identify
the pathogen. Conidiophores were cylindrical, 70–145 × 6–8.5 µm,
moderately flexuous to straight in foot-cells and produced conidia
singly, followed by 2–3 cells (Fig. 1B–D). Appressoria were
multilobed or moderately lobed (Fig. 1J). Conidia were oblong-
elliptical, 28–54 × 11–18 µm, without conspicuous fibrosin bodies
and produced germ tubes in the perihilar position (Fig. 1F–I). First-
formed conidia (Fig. 1E) were apically conical, basally subtruncate,
and generally smaller than the secondary conidia. No chasmothecia
were found but the above characteristics were consistent with the
conidial state of Erysiphe aquilegiae DC. (Braun, 1987; Liberato
and Cunnington, 2006).
To confirm the identity of the causal fungus, the complete internal
transcribed spacer (ITS) region of rDNA from KUS-F24744 was
amplified using primers ITS5 and P3, and then directly sequenced.
The resulting sequence of 553 bp was deposited in GenBank
(Accession No. JN003594). Phylogenetic analysis was performed
using MEGA4 with the neighbor-joining method and the Tajima-
Nei distance calculation. A comparison with the sequences
available in the GenBank database revealed that the ITS sequence
shared over 99% (552/553 bp) similarity with those of E. aquilegiae
on several host genera of the Ranunculaceae (Fig. 2). Therefore, the
sequence analysis verified that the pathogen was E. aquilegiae.
Powdery mildew caused by E. aquilegiae has been shown to
occur on plants belonging to the Ranunculaceae with one exception
(Farr and Rossman, 2011). Catharanthus roseus (L.) G. Don, which
belongs to the Apocynaceae, was found to be naturally infected by
E. aquilegiae as demonstrated by morphological and molecular data
(Liberato and Cunnington, 2006). To the best of our knowledge, this
is the second report where E. aquilegiae was found on a host outside
of the Ranunculaceae. An occurrence of powdery mildew disease
on this tree was previously recorded in Argentina; however, in that
study, the causal fungus was not identified (Mantz et al., 2008).
Their description of the causal fungus was actually identical to the
characteristics reported here. Therefore, we believe that their fungus
was also E. aquilegiae.
References
Braun, U. 1987. A Monograph of the Erysiphales (Powdery Mildews).
Beih. Z. Nova Hedwigia 89:1−700.
Farr, D. F. and Rossman, A. Y. 2011. Fungal databases, systematic mycol-
ogy & microbiology laboratory, ARS, USDA. Retrieved May 18, 2011,
from http://nt.ars-grin.gov/fungaldatabases/.
Liberato, J. R. and Cunnington, J. H. 2006. First record of Erysiphe aquile-
giae on a host outside the Ranunculaceae. Australas. Plant Path.
35:291−292.
Mantz, G., Ronco, L. and Monaco, C. 2008. First record in Argentina of
powdery mildew of Casuarina cunninghamiana caused by Oidium sp.
J. Plant Pathol. 90:397.
*Corresponding author (hdshin@korea.ac.kr)
Disease Report Open Access
Fig. 1. Powdery mildew infections of Casuarina cunninghamiana by
Erysiphe aquilegiae. (A) Close-up view of infected leaves. (B–C) Coni-
diophores with immature first-formed conidia. Note the conically rounded
apex. (D) A conidiophore with an immature secondary conidium. Note
the subtruncate apex. (E) A first-formed conidium. (F–H) Conidia. (I)
Germinating conidium. (J) Hypha with multilobed appressoria. Each
structure in B–J was stained with lactofuchsin. Bar = 50 µm for B–D and
20 µm for E–J.
Fig. 2. Neighbor-joining tree showing the phylogenetic relationship
among Erysiphe aquilegiae isolates inferred from the ITS rDNA region.
Bootstrap values based on 1000 replications are indicated above the
branches, and the scale bar represents 0.02 nucleotide substitutions per site.
