Pathogenicity and vegetative compatibility grouping among Indian populations of Fusarium oxysporum f. sp. ciceris causing chickpea wilt

Thirty-nine isolates of Fusarium oxysporum f. sp. ciceri – the causal agent of chickpea (Cicer arietinum) wilt – collected from different parts of India and representing eight races of the pathogen, were analyzed for virulence and classified on the basis of vegetative compatibility grouping (VCG). The wilt incidence ranged from 24% to 100% on a highly susceptible cultivar JG 62. Six isolates, from Delhi, Gujarat, Karnataka, Punjab and Rajasthan and belonging to six different races of the pathogen, caused 100% wilt incidence. Five isolates belonging to four different races, namely, Foc 143 from Andhra Pradesh, Foc 161 from Chhattisgarh, Foc 146 from Karnataka, Foc 158 from Madhya Pradesh and Foc 50 from Rajasthan, caused low wilt incidence. For VCG analysis, nitrate non-utilizing mutants (nit) were obtained by culturing wild-type isolates on 2.5% potassium chlorate and selecting resistant sectors. Complementary nit mutants were paired in all possible combinations to determine varying degrees of heterokaryon formation within the isolates, which showed that most of the isolates were self-compatible. Pairing of all the mutants showed that the isolates included in the present study belonged to a single VCG (0280). Thus, in spite of variability in the virulence, the Indian populations of the pathogen have only one VCG.