The role of a fadA ortholog in the growth and development of Colletotrichum graminicola in vitro and in planta

A transposon-based split-marker protocol was used to produce insertional mutations in the fadA ortholog of the maize anthracnose pathogen Colletotrichum graminicola. The mutants grew more slowly in culture, produced fewer oval spores, produced fusiform rather than falcate phialospores, lost their normal clockwise spiral growth pattern in culture, and were significantly reduced in their pathogenicity to maize stalks and leaves. The differential effect of the fadA mutation on oval spore versus phialospore production suggests that there are differences in the signaling pathways that regulate these two types of sporulation. It has been suggested that oval spores function in anthracnose lesion extension. In maize stalks, production of oval spores appeared to be relatively unaffected in the mutant strains, but production of vegetative hyphae and elongation of primary lesions were both reduced. This suggests that vegetative hyphae play a more important role than oval spores in primary lesion development. However, production of discontinuous secondary lesions in maize stalks infected by mutant strains did not appear to be seriously affected, and thus oval spores may play a more important role in that process.