Introduction to Fungi, Third Edition

GLOMERELLACEAE
387
Fig12.51 Colletotrichum graminicola. (a) Portion of Sorghum
grain bearing acervuli. (b) An acervulus. (c) Phialides and
phialoconidia.
teleomorph genus, Glomerella, which consists of
five species, and numerous species belonging
to the form-genus Colletotrichum. Early workers
defined Colletotrichum spp. mainly by their association
with host plants, so that approximately
750 ‘species’ were described before von Arx (1957)
tidied them up by synonymizing them into
11 taxa. For C. gloeosporioides alone, von Arx
(1957) recognized 600 synonyms. A more recent
treatment is that by Sutton (1992) in which
39 species are described. Many of these are
probably species complexes, and for example
six formae speciales have been described for
C. gloeosporioides.
Glomerella forms dark-walled perithecia which
occur singly. They are long-necked and release
ascospores passively. The Colletotrichum state is an
acervulus, i.e. a saucer-shaped conidioma which
develops within the host tissue, rupturing
the cuticle at maturity (Fig. 12.51a). The
conidiogenous cells form a closely packed palisade
of phialides (Fig. 12.51c). The curved
elongated phialoconidia are produced in a
slimy droplet which is held in place by stiff
dark setae surrounding the acervulus (Fig.
12.51b). This mucilage contains the autoinhibitor
mycosporine-alanine which prevents the
germination of conidia until it has been diluted
out (Leite & Nicholson, 1992). Other germination
autoinhibitors are localized within the conidial
cytoplasm of diverse Colletotrichum spp. (García-
Pajón & Collado, 2003). The presence of such
substances explains why the spores of many
fungi germinate better after they have been
washed.
Mating systems are complex and variable in
Glomerella. For example, in G. cingulata (anamorph
C. gloeosporioides), both homothallic and heterothallic
strains occur, and there may be more
than two mating type idiomorphs (Cisar &
TeBeest, 1999). The occurrence of multiple alleles
at one mating type locus is common in the
Basidiomycota but has apparently not been
found in any ascomycete other than Glomerella.
Many strains belonging to a given species