Cultural Characteristics And Pathogenicity Differentiation Among Strains Of Verticillium Dahliae From Cotton In Xinjiang

Xinjiang is the largest cotton planting area in China.In the past five years,cotton Verticillium wilt has developed more rapidly,and there has been an explosive development trend,which seriously threatens the development of cotton industry in Xinjiang.It is urgent to determine the occurrence and distribution of defoliating strain and non-defoliating strain of Verticillium dahliae in cotton fields,cultural characteristics on PDA media and pathogenicity differentiation of V.dahliae.Therefore,in this study,V.dahliae collected from different cotton areas in Xinjiang were used to identify defoliating strain and non-defoliating strain,physiological race and mating type,to analyze the occurrence and distribution of different pathotypes,to compare culture characteristics on PDA of representative strains and their virulence to cotton.The main results are as follows:1.The total of 852 cotton plants displaying Verticillium wilt were collected from different cotton planting areas in Xinjiang,the results of PCR identification showed that all strains isolated from infected cotton plants determined to be V.dahliae with specific primer pair VDS-F and VDS-R for V.dahliae.The results of pathotypes detection showed that defoliating strains and non-defoliating strains accounted for 65.3% and 27.7%,respectively,7.0% strains could not be classified into defoliating or non-defoliating strains,indicating that the pathogenic types of the tested strains were differentiated,among which defoliating strain was the main pathotypes.Field plots were analyzed according to the proportion of the defoliating and non-defoliating strains in every plots.Analysis of field plots showed that the plots only with defoliating strains were the most,then mixed plots with defoliating strains and non-defoliating strains.67.9% of the field plots were dominated by defoliating strains,suggesting that defoliating strains has become the main pathogenic type in the fields.2.The total of 140 representative strains of V.dahliae were chosen to determine their physiological races and mating type.The results showed that all the strains were physiological races 2,and their mating type were MAT1-2.At the initial stage of strain isolation,the culture phenotypes of 400 V.dahliae strains were analyzed.The results showed that sclerotium type strains accounted for 79.2%,the intermediate type strains accounted for 17.2%,and the mycelium type strains accounted for 3.6%.The culture characteristics variation maybe exist in one strain isolated from a single conidium.The results of cultural characteristics on PDA media showed that 23 representative strains produced three colony morphologies: sclerotium type,hyphal type and intermediate type.Sclerotium type colony was the main culture type and further differentiated into three different colony types.3.The infection assays displayed that the average disease index of cotton seedling infected with defoliating strains was higher than that of non-defoliating strains,and there were strains with high disease index among the non-defoliating strains.There are significant differences of virulence in different strains from the same region.It indicated that differentiation of virulence exist in in V.dahliae strains from cotton fields in Xinjiang.The above results show that the differentiation of pathogenic types,culture characteristics and virulence exist in strains of V.dahliae from cotton field in Xinjiang.