Study On The Cultural Characteristics And Pathogenic Differentiation Of Veticillium Dahliae From Cotton In Henan

Cotton Verticillium wilt that caused by Verticillium dahliae Kleb is one of the most important diseases of cotton in China,which seriously threatens the sustainable development of cotton production.The pathogenicity of Veticillium dahliae differentiate in China,but at present which still was not clear in Henan.In order to intentify the pathogenicity of Verticillium dahliae in Henan Province,37 strains of Verticillium dahliae were isolated,purification and identification from diseased cottons collected from main cotton production areas in Henan Province.The culture characters and pathogenicity of 37 strains and their crude toxin were studied.According to the assay of culture characteristics,Verticillium dahliae strains in Henan province could be divided into three types:sclerotium type,middle type and filamentous type.The colony characteristics of sclerotium type:the white colonies surrounded by all black,dense mycelium showed villiform or sponge-like and colonies were circular or radial,produced a lot of micro-sclerotia; there are 27 strains belonging to this type among the 37 strains,accounting for 73%.The filament type:Colony surface was white or light yellow,the bottom was light yellow,the texture was hard and mycelium was developed,didn't produced micro-sclerotium after culturing 2 weeks;2 strains belonged to this type and accounted for 5.4%among the testing strains.The middle type have smooth edge of the colony,produced a small amount of micro-sclerotia and mycelial.8 strains belonged to this type in the 37 strains and accounted for 21.6%.The virulence of the 37 strains of Verticillium dahliae and T-9,V246 strain on two cotton varieties were determined respectively by root inoculation injury in greenhouse.The results showed that the virulence variation of strains from different regions was significant.According to the results of pathogenicity,Verticillium dahliae strains in Henan province could be divided into three pathogenic types:severe virulent type,intermediate virulent type and mild virulent type accounting for 56.8%,24.3%,18.9%respectively.The virulence of Verticillium dahliae in Henan showed differentiation among the strains from different regions in Henan,and the virulence of the strains from the same place also had certain differences. The results of cmparing Verticillium dahliae culture characteristics with virulence indicat that filamentous type strains have strongest virulence and the mean disease index is 46.98;the mean disease index of sclerotium type strains with the middle virulence was 42.29;the middle type strains have the weakest virulence and the mean disease index of 8 middle type was 12.59.The sclerotium diameter of the sclerotium type strains and the mean disease index on two cotton varieties was positive correlation which correlation coefficient was 0.7665 and reach a significant level.This indicates that the growth of the strain's sclerotium was more quickly,it's virulence was more strong and with the higher mean disease index,on the contrary,the strains with the the smaller sclerotium diameter have the weak virulence.Seeing from the colony cultural characteristics,the virulence of the strains with the majority of thick colony,dense mycelial pathogenic strains was highly,while the virulence of the strains with the colony which thin and sparse hyphae has less virulence.The pathogenic capacity of crude toxin from different strains were tested.The results showed that the crude toxin of Verticillium dahliae strains had strong pathogenic ability.When cotton seedlings in the crude toxin with water in the ratio of 1:10 showed the same wilting symptoms as the pathogen infection symptoms.The degree of wilting increased with time passing,and reached stable value after 96 hours.The result of correlation analysis of pathogenicity testing by innoculation of Verticillium dahliae and the capacity of wilting by crude toxin showed that the correlation coefficience up to 0.8253,and the difference reached significant level.These results shows that the crude toxin and the pathogenicity of Verticillium dahliae Kleb is closely related,the higher wilting index,the stronger virulence,and vice versa.