Prevalence of the Defoliating Pathotype of Verticillium dahliae on Cotton in Central China and Virulence on Selected Cotton Cultivars

Three hundred and forty-one isolates of Verticillium dahliae from upland cotton collected from 2007 to 2009 in central China (Hubei, Hunan, Jiangxi, Anhui and Jiangsu provinces) were tested for vegetative compatibility groups (VCGs) and PCR-based genotyping. Approximately 332 (97%) isolates belonged to VCG1A, whereas the remaining 9 (3%) isolates belonged to VCG2. PCR-based genotyping also divided the isolates into two groups, namely PCR patterns A and C. There is a complete correspondence between the VCGs and genotypes (VCG1A to PCR pattern A and VCG2 to PCR pattern C). Representative isolates (10 VCG1A isolates, nine VCG2 isolates) were tested for virulence on seedlings of upland cotton (Gossypium hirsutum cultivars E Mian 24 and Yin Rui 361). The VCG1A isolates caused cotton defoliation with the values of the disease severity index and the plant mortality being significantly (P < 0.05) higher than those caused by the VCG2 isolates, which did not cause any defoliation. Two isolates (one of each VCG) were also tested for virulence on 12 popular commercial upland cotton cultivars adapted in central China. Results showed that both isolates, particularly the defoliating pathotype (D pathotype) VCG1A isolate, were virulent on all the tested cotton cultivars. These results suggest that the D pathotype of V. dahliae is widely distributed and has become prevalent in central China.