Characterization of conidiation mutants in Glomerella graminicola

The maize pathogen Glomerella graminicola (anamorph: Colletotrichum graminicola) is a hemibiotroph with a life cycle that includes the production of two distinct types of conidia. One type is falcate-shaped, and the other is oval-shaped. Production of falcate conidia is light-dependent for wild-type strains. One hour of light exposure (170 $\rm mM/m\sp2/s)$ is both essential and sufficient to produce normal levels of falcate conidia. I have characterized two classes of isolates in which light-regulation of falcate conidia is abnormal. The $\rm Con1\sp-$ phenotype produces comparable numbers of falcate conidia in the dark and light. In contrast, the $\rm Con2\sp-$ phenotype produces few falcate conidia in either the light or the dark. Genetic analyses with random ascospores indicated that each mutant phenotype results from a single gene mutation. The Con2 locus is linked to Pyr1 at 18 cM, and Con1 is not linked to Pyr1 or any other markers. A RAPD marker which is linked to Con2 at 9 cM has been identified using bulked-segregant analysis. A genetic map of the three markers, Con2, Pyr1, and A08 was constructed. In an attempt to clone the Con2 gene, the $Con2\sp-$ mutant was complemented with the genomic library of the wild-type, and a transformant which produced wild-type level of falcate conidia was recovered. I have also examined a class of mutants that were generated by insertional mutagenesis. These mutants lack the ability to produce wildtype levels of oval conidia. Interestingly, these mutants have an array of general developmental defects including abnormal appresorium formation, and they display greatly reduced pathogenicity