Nitrate-nonutilizing mutants used to study heterokaryosis and vegetative compatibility in Glomerella graminicola (Colletotrichum graminicola)

Nitrate-nonutilizing (nit) mutants of Glomerella graminicola were recovered by selecting chlorate-resistant sectors. Heterokaryons were formed by complementation between two different classes of nit mutants. Complementation groups were distinguished in nitrogen feeding tests and segregated as two, unlinked genes among random progeny of sexual crosses. The two genes are comparable to those encoding the nitrate reductase enzyme and one of a series of molybdenum cofactors in Aspergillus nidulans and Neurospora crassa. Heterokaryon tests were reliable indicators of allelic and dominance relationships between mutations with similar phenotypes. Vegetative compatibility (VC) between two strains of G. graminicola appeared to be regulated by approximately five unlinked VC loci, analogous to those described for other fungi.