García,V.M., Thon, M.R. and Sukno, S.A. 2006. 8th European Conference on Fungal Genetics (ECFG). Vienna, Austria. April 7-12, 2006.
Colletotrichum graminicola (Ces.) G. W. Wils. causes anthracnose stalk rot, top
die-back and leaf blight of maize. The pathogen survives in residue on the soil
surface, in buried residue, and as sclerotia (stromata) inside stems on the soil.
Little is known about its role as a root pathogen though it has been suggested
that C. graminicola can infect maize roots in the field. Recent literature suggests
that many fungi that are commonly regarded as causal agents of foliar diseases
can also cause systemic infection of their hosts by invading roots. We are
investigating the importance of root infections of C. graminicola on the
anthracnose disease cycle. Maize seeds were grown in vermiculite that had been
inoculated with mycelial agar plugs of C. graminicola isolate M1.001BH. Three
weeks after sowing, the roots of the seedlings were washed, sectioned, and
visualized with light and fluorescent microscopy. Lesions on the roots were not
observed, however fungal hyphae could be found colonizing the surface of the
roots and invading epidermal cortex and vascular tissue. Structures, typically
formed by root pathogens but not previously reported for C. graminicola on
roots, including hyphopodia and microsclerotia were observed. Certain epidermal
and cortical cells become infected from intercellular hyphae while surrounding
cells are uninfected, resulting in a mosaic pattern of infection. Interestingly,
conidia were formed in acervuli on the root surfaces but were also found filling
epidermal cells and root hairs. Preliminary data indicate that root infections
cause significant stunting of both roots and above ground portions of seedlings
and that the fungus can spread from the roots to aerial tissues. These
observations suggest that root infection may be an important component of the
maize anthracnose disease cycle.
Poster