Epidemiology of verticillium wilt of cotton: Pathogenicity variation among isolates Verticillium dahlia

In order to determination of variability of pathogenicity of Verticillium dahliae kleb., Ninety five isolates form soil, cotton, eggplant, okra, cucumber, pistachio, sesame, tomato, and wild hemp, and rhizospher of Datura stramonium, Xanthium sp. and Solanum nigrum were compared in respect to microsclerotial morphology,pathogenicity, host range, optimum temperature for growth and vegetative compatibility groups (VCGs).The result showed that based on symptom in cotton and okra plants the isolates were divided in two defoliating and no defoliating strains which also differed in microsclerotial morphology on water agar, optimal temperature for growth on potato dexteros agar. The variability among no defoliating isolates were more than defoliating isolates. Although, there was not host specificity among isolates but observed various disease severity in cotton .The defoliating strains were collected from cotton, eggplant, sesame and soil in Estahban, Kord kuy and Varamin regions. From 52 nit mutants (54%) were obtained 95 isolates. Based on the ability to use different nitrogen sources the mutant were grouped into three phenotypic classes nit 1(25%), nit 3(12%) and nit M( 54%).The isolates were separated into different groups. Eight VCGs were recognized among nit mutants. All defoliating isolates were belonged to one VCG and rest of the isolated grouped in 7 VCGS.