| Cotton Verticillium wilt(Verticillium wilt)is a typical soil-borne and vascular fungal disease.Because of the difficulty of prevention,it is also called "cancer" on cotton.The main methods to control cotton Verticillium wilt are breeding resistant varieties,chemical control,agricultural control and biological control.Biological method to control Verticillium wilt has attracted lots of attention in recent years.The discovery and application of attenuated fungal viruses provided a useful supplement for biological control,and fungal viruses were successfully used to treat chestnut blight and Sclerotinia sclerotiorum.Therefore,screening related viruses which can cause virulence decline from cotton Verticillium dahliae is expected to provide new virus resources for the biological control of cotton Verticillium wilt.It was found that there were significant differences in virus types between virulent and low virulent strains of Verticillium dahliae.In this study,10 strains of single spore progeny with strong pathogenicity and weak virulence were sequenced by high-throughput macrovirus groups on the basis of defining the pathogenicity of the strains.The results showed that cotton Verticillium dahliaeincludes abundant virus species.Most of them have not been reported or cleared the taxonomic status.A total of 42 viruses are obtained among the 10 weakly virulent strains,which can be divided into positive single-stranded RNA virus,negative single-stranded RNA virus,double-stranded RNA virus and unclassified viruses according to the nucleic acid type.Among them,single-stranded RNA viruses account for 52%,dsRNA viruses account for 19%,and unclassified viruses account for 29%.Only 1 virus was carried in the virulent strains as negative single-stranded RNA virus according to the type of nucleic acid.Through the comparison of the virus types of two different pathogenic strains,it was found that there was a positive correlation between the pathogenicity of the strains and the number of fungal viruses.The type and number of viruses carried by weak pathogenic strains are obviously richer than those carried by strong pathogenic strains.In summary,the types of viruses carried by weak pathogenic strains are rich,while those carried by strong pathogenic strains are few and simple.It was found that the low virulent strains were co-infected with the virus,and the biocontrol potential of the virus was evaluated.Through the RT-PCR verification of the virus sequence in the weakly virulent strains,the types of viruses in each strain were identified.All the low virulent strains were infected by multiple viruses.A virus was found to be existed in multiple strains at the same time.Among the weakly virulent strains,the members that belong to Ourmiavirus were the most distributed.The viruses that belong to Tombusviridae were the least.Among those,the viruses which belong to Tombusviridae,Ourmiavirus and Mitoviridae were reported in cotton Verticillium dahliae for the first time.Through confrontation culture between weakly pathogenic strains and hygromycin resistant virulent strains,the virus was transfered into virulent strains.According to the results of virulence test,it was preliminarily inferred that the virus could be transmittedhorizontally through mycelial fusion in cotton Verticillium dahliae,and the virulence of weakly virulent strains were decreased significantly after being introduced into virulent strains.In this study,through the using of high-throughput sequencing technology,there were a large number of viruses in cotton Verticillium dahliawas found,and a great difference between weak pathogenic strains and strong pathogenic strains were detected.The viruses in weak virulent strains were weakly virulent.The results of this study could enrich the species of fungal viruses,provide virus resources for virus evolution studying and enhance the use of fungal viruses to control Verticillium wilt on cotton. |
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