Twenty five isolates of Colletotrichum gloeosporioides obtained from fruits of olive, apple and citrus trees from different regions of Golestan province, northern Iran. Results from cross-inoculation experiments showed a great variability in pathogenicity among the isolates examined. They were investigated using complementation tests with nitrate-non-utilizing (Nit) mutants to know their vegetative compatibility. Among 250 chlorate-resistant sectors obtained, only 187 were Nit mutants. Three types of Nit mutants were obtained (Nit1, Nit3and NitM) on the basis of the fungal phenotype. Nit1 mutants were the most frequent (71.6%), followed by NitM (16.6%) and Nit3 (11.8%). Based on their ability to form heterokaryons, all olive pathogenic isolates were grouped into two vegetative compatibility groups (VCG). This is a good indication of the homogeneity of the olive C. gloeosporioidespopulation. The results might also suggest the absence of a relationship between pathogenicity of strains on apple and VCG.
Key words: Nit mutants, VCG, Colletotrichum gloeosporioides, Olive tree.
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