Abstract:Verticillium wilt is one of most important diseases in cotton. In order to explore the population construction and pathogenicity differential characteristics of Verticillium dahliae of cotton, the pathogenicity testing for 43 isolates of V.dahliae collected from same cotton field was examined by five differential hosts with symptom reaction and disease index evaluation. The result showed that isolates of V.dahliae had obviously pathogenicity differentiation and can be divided into three physiological types: TypeⅠcausing a severe defoliation with strong pathogenicity, Type Ⅱ causing mixed symptoms with intermediate pathogenicity, Type Ⅲ causing none defoliation with weak pathogenicity. Among them, isolates of TypeⅠ , Type Ⅱ and Type Ⅲ occupied 44.2%, 37.2% and 18.6% of total examined isolates and the average disease index of them was more than 50, between 30 to 50 and less than 30, respectively. It indicated that V.dahliae in naturally infested soil existed as the form with high variation and mixed genotypic population, and each of sub group population had various pathogenicities.