NITRATE NON-UTILIZING MUTANTS OF COLLETOTRICHUM AND THEIR USE IN STUDIES OF VEGETATIVE COMPATIBILITY AND GENETIC RELATEDNESS

Seven strains from five different Colletotrichum species were tested for their ability to produce chlorate-resistant nitrate non-utilizing mutants when cultured on potato-dextrose agar (PDA) or on a minimal medium containing 1.5% KClO3. Six of the seven strains produced mutants that could be placed into one of four phenotypic classes representing mutations at: the nitrate reductase structural locus (nit1), the global nitrogen regulatory locus (nit2), the nitrate-assimilation pathway-specific regulatory locus or the nitrite reductase structural locus (Nit3), and the loci that affect the assembly of a molybdenum-containing cofactor necessary for nitrate reductase activity (NitM). The seventh strain (C. malvarum) was sensitive to nitrite and the test to distinguish the nit1 class from the Nit3 class could not be performed. Five of the strains examined were heterokaryon self-compatible since paired complementary nit mutant strains could form prototrophic heterokaryons. Although both intragenic and intergenic complementation occurred, some of the nit mutant sectors were unable to complement with any of the other nit mutants derived from the same culture. Strains of C. destructivum and C. fragariae were heterokaryon self-incompatible because none of the nit mutants were able to form a heterokaryon when paired on minimal medium containing nitrate as a sole nitrogen source. The five heterokaryon self-compatible strains were all in distinct vegetative compatibility groups since complementary nit mutants from different strains could not form a prototrophic heterokaryon when cultured on minimal medium with nitrate as the sole nitrogen source.