GENETIC-ANALYSIS OF 2-RACE-0 X-RACE-2 CROSSES IN COCHLIOBOLUS-CARBONUM

Progeny from two crosses of race 0 X race 2 of Cochliobolus carbonum segregated in 1:1 ratios for loci controlling mating type, fungicide tolerance, and ability to sporulate on potato-dextrose agar. Segregations at single loci also were observed for three isozyme systems and for one of two bands in a fourth system. Progeny also segregated for four esterase bands, but the segregation patterns were complex. Pathogenicity to corn was inherited as two apparently complementary genes present in race 2 but lacking in race 0, which was avirulent on corn. Evidence was found for a new locus for production of pseudothecia and a new locus for production of asci and ascospores. These putative loci differ from the previously described single loci for pseudothecium and ascospore production in C. carbonum. Gene mapping analysis identified two linkage groups: one 11 cM (centiMorgans) long with two linked loci for esterase bands, and one 164 cM long with six loci including the mating type locus, one locus for cadmium tolerance, and two loci for esterase bands. A quantitative trait locus for conidium production was found within 2 cM of the Est-B92 locus of the larger linkage group. The frequency distributions among race 0 X race 2 progeny for the numbers of conidia and pseudothecia produced were skewed toward poor production by most of the progeny relative to the parents.