Abstract:To explore the pathogenicity differentiation and variability of Verticillium dahliae population from cotton in northern Xinjiang, 41 representative strains were collected and the pathogenicity type were determined on the basis of differential host tests and PCR assay. The results of special PCR primer (ND1/ND2 and D1/D2) assay showed that the defoliating and non-defoliating strains occupied 39.0% and 58.5% of total examined strains, respectively. The results of inoculating differential host tests showed that strong, medial and weak pathogenicity strains occupied 51.2%, 29.3% and 19.5% of total examined strains. Generally, the symptoms infected by the defoliating strains are more severe than non-defoliating strains, and the corresponding average index was 39.4 and 25.8. Defoliating symptoms have manifested in cottons infected by defoliating and non-defoliating strains. Thus, the defoliating symptom is not only related with the pathogenicity and pathotype of pathogens, but also with the resistance of cotton cultivars.