The Variation Among Progeny Isolates Of Verticillium Dahliae Vd076 In Field And Its Relationship With Selective Pressure Of Host

Verticillium dahliae.Kleb.,the pathogen of Verticillium wilt on cotton,causes significant economic losses in the cotton production area worldwide.The pathogenicity differentiation of this pathogen easily takes place,which usually causes the resistance lose of cultivars to the pathogen.To date,Verticillium wilt is still a major problem on cotton production,and there is no effective management strategies for controlling it.In the present study,V.dahliae single spore progenies were isolated from disease nursery which inoculated single spore isolate Vd076 and cultivated resistance and susceptible varieties for more than 8 years;and the physiological characteristics,pathogenic types,physiological races,variation of population genetics of the single spore progenies were studied.Furthermore,the relationship between its mutation and the host selection was assessed in the grenhouse trails.The main results are as follows:1.According to the cultural type,all of 90 progenies of Vd076 were divided into three types,sclerotium type,filamentous type and moderate type.the moderate type was the main type(64.4%).The isolates with significant changes were all significantly higher than the Vd076.2.Pathogenicity test showed that all of 90 progenies of Vd076 were divided into three types,strong,moderate and weak,while the average of the disease index were from 13.6 to 65.7.The isolates with strong pathogenicity and moderate pathogenicity consitituted the majority of the progeniy populations.The virulence range of isolates isolated from tolerant varieties was wider than that from susceptible varieties.Molecular detection showed that all tested isolates were defoliating isolates and belong to race 2,which were no variation compared with Vd076.3.The genetic structure and genetic diversity of the tested isolates were analyzed with the 14 screened primers in ISSR,Nei's gene diversity was 0.2778 while Shannons information index was 0.4213,which suggested that relatively rich genetic diversity in the whole population.The isolates with strong pathogenicity had a higher genetic diversity than other two groups.Based on the clustered analysis,the population genetic diversity was not consistent with the culture feature and pathogenicity of the isolates.4.The results of the whole genome resequencing of tested isolates showed that there were 109,223 SNPs,1,067,133 Indel,35,714 SV and 2,969 CNV.The ratio of nonsynonymous substitution to synonymous substitution(Ka/Ks)of most progenies were about 0.6,which were undergoing negative selection effect.The progenies of Vd076 had variation of different degrees,and the variation level of the progenies of Vd076 was relatively high.The four isolates with relatively less variation were all of the weak and moderate pathogenic types.5.V.dahliae isolate Vd076 with moderate virulence was subinoculated on resistant cotton cultivars(Zhongzhimian2)for 7 generations and susceptible cotton cultivar(Jimian11)for 7 generations,and alternately inoculated on resistant and susceptible cultivar for 7 generations,to study the impact of the selective pressure of host on the virulence.The results showed that resistant cultivars significantly induced the virulence increase after 5 generations,while inoculated susceptible cultivar and alternately inoculated did not obviously induce the pathogenicity changes during 7 generations.These results suggested that the progenies of V.dahliae Vd076 were discrepant in cultural features,pathogenicity and genetic diversity,and the resistant cultivars significantly induced the virulence increase of V.dahliae.The results provided the scientific evidence for monitoring the early variation of V.dahliae under natural conditions and rational distribution of disease-resistant varieties in the field.