Genus Cercospora in Thailand: Taxonomy and Phylogeny (with a ...

Plant Pathology & Quarantine
Fig. 4 – Various types of conidia of the true cercosporoid fungi sensu Crous & Braun (2003) found
in this study (40×) (black arrows: conidia hila, white arrows: septation). a. Conidia of genus
Cercospora s. str. b. Conidium of genus Passalora. c. Conidia of genus Pseudocercospora.
(Meeboon 2009).
locus or unilocal) or polyblastic (with two or
more conidiogenous loci or multilocal), formed
either synchronously or, mostly; in a sympodial
succession (Hennebert & Sutton 1994). Conidiophores
(or conidiogenous cells) can be
determinate (growth ceasing with the production
of a terminal conidium or conidial chain)
or they can proliferate [indeterminate, proliferation
being sympodial or percurrent (through
the open end left when the first conidium
becomes detached)] (Hennebert & Sutton
1994). Cercospora is characterized by having
blastic (monopolyblastic), schizolytic, and
sympodial proliferation (Crous & Braun 2003).
C. Conidia
The important characters of conidia of
the genus Cercospora are mostly related to the
shape, septation, pigmentation and surface
(Figs 4a–c), similar to the Saccardoan system
(Crous & Braun 2003). The conidia of Cercospora
species are either straight to curved, and
acicular, filiform, obclavate or a combination
of shapes (Crous & Braun 2003). There are two
basic types of septation, viz, euseptate (septa
formed by all existing wall layers) and
distoseptate/pseudoseptate (septa formed only
by the innermost layer) (Hennebert & Sutton
1994). The term septum (septate) without
specification is usually applied to euseptate
(Hennebert & Sutton 1994).
Hyaline and pigmented conidial structures
are usually well separated in certain taxa
(genera, species) of the cercosporoid fungi, but
transitional phenomena are not uncommon
(Crous & Braun 2003). However, taxa with
subhyaline to pale (yellowish green, pale olivaceous,
etc.) structures often cause serious
taxonomic problems (Crous & Braun 2003).
The conidia of Cercospora are characterized by
hyaline or pale olivaceous pigmentation and
euseptate conidial septation (Crous & Braun
2003)
Collection and Observation
Specimen collection involved an observation
of the presence/absence of the fruiting
bodies/caespituli on the leaf. The observation
was usually conducted using a 10× or 20×
magnifying lens. Specimens that are positively
showed the presence of Cercospora fruiting
bodies/caespituli were placed in plastic bags.
The collecting bags were sealed and labeled:
Name of host plants, Collection site, Collector
/s, and Collection date.
Detailed observations of morphological
characters were generally carried out by means
of a dissecting microscope, followed by light
compound microscope using oil immersion
(1000×). Specimens for microscopic observation
were prepared by hand sectioning or fine
forceps. Water is very good as mounting medium.
Shear’s solution or lactophenol was
usually used as a media for permanent slides.
Thirty conidia, hila, conidiophores, conidiogenous
loci and 10 stromata were commonly
measured for each specimen. Line drawings
were prepared at a magnification of 400×, or
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