STUDYING VEGETATIVE COMPATIBILITY IN VERT ICILLIUM-DAHLIAE KLEB WITH NON-NITRATE-UTILIZING MUTANTS

Sixty strains of Verticillium dahliae isolated from seven host plants in 11 countries were tested for vegetative compatibility (VC) with nit rate non-utilizing (nit) mutants. These nit mutants were obtained from wild-type strains by selecting chlorate-resistant sectors on media co ntaining potassium chlorate (15 g/l). Inhibition of radial growth vari ed from 20% to 80% in different strains. Distribution of nit mutants w as the following. Nit M, 37.2%, nit 1, 41.0%, and the others, 21.8%. V . dahlias nit mutants from cotton isolates had the same virulence as t he initial strains. Tests for VC revealed four vegetative compatibilit y groups (VCG): VCG1 included 57 strains, and each of the other three, included only one strain. VCG1 was divided into five subgroups. All s trains of cotton-wilt causal agent from Central Asia represented by ra ces 0, 1, 2, 3, and 4 were compatible with each other and tester strai n T-9 from California (GVC1). Diversity in virulence within the same V CG confirms that new races of cotton-wilt causal agent may appear as a result of parasexual cycle, The obtained data show that physiological races often are not isolated genetically, in contrast to specialized forms.