Genetic variations of prevailing Verticillium dahliae isolates from cotton in China

Abstract

Verticillium wilt caused by the soil-borne fungus Verticillium dahliae is a devastating disease of cotton, leading to serious loss of lint yield in China. It is important to characterize the prevailing populations of V. dahliae for understanding disease development. In this study, the representative 74 V. dahliae isolates from 28 different cotton regions in three major cotton-production areas in China were identified for their pathotypes, races, vegetative compatibility groups (VCGs) and genetic diversity by specific PCR, amplified fragment length polymorphism (AFLP) and inter simple sequence repeat (ISSR) analysis. Of 74 isolates, 60 isolates (81%) were defoliating (D) pathotype strains, especially in Yellow River/Yantze River Valley region. Seventy isolates belonged to race 2, whereas no race 1 specific fragment was amplified. These isolates were grouped into five VCGs: VCG1A (48), VCG2A/VCG4B (3), VCG2B824 (6), VCG6 (5). The D pathotype and VCG1A isolates have become the dominant strains, moderately and highly virulent isolates were widely distributed in three major cotton-growing areas in China. High level of polymorphic markers was obtained by AFLP and ISSR analyses. Through comparison of the obtained dendrograms by unweighted paired group method with arithmetic averages cluster analysis (UPGMA), the V. dahliae isolates were divided into two major groups and five subgroups. The obvious correlations with the geographic origin of the isolates between AFLP and ISSR were revealed, with significant diversity among V. dahliae isolates. In addition, AFLP dendrogram showed relationships with pathotypes. The results offered a better understanding of the epidemiology of Verticillium wilt in China.