Distribution Of Defoliating Pathotype And Toxicity Test Of Verticillium Dahliae In Shandong Province And Screening Of Biocontrol Bacterium

Cotton Verticillium wilt, caused by Verticillium dahliae.Kleb, is the most serious diseases in cotton production in Shandong Province. The diseased area was more than46.7hectares every year and caused huge economic losses and impact on cotton production directly. Pathogenicity of the pathogen has changed significantly in recent years especially the defoliating (D) type was found widely distributed in China. But there is no information available about its distribution in Shandong Province. So it’s very significant to understand the characteristics of defoliating type strains and their distribution in Shandong province for controlling the occurrence and spread of V. dahliae effectively.In this research, samples were firstly collected from Dezhou, Dongying and Taian in Shandong province and202strains were isolated and purified. Subsequently, we analyzed the distribution of defoliating (D) type of V. dahliae in Shandong Province in combination of morphological and molecular characterizations. Also, capacity of toxin production and virulence of selected strains were performed and different. At last,9antagonistic bacterial isolates were screened and identified from different soils to V. dahliae. The results are as follows:1. We collected Cotton verticillium wilt samples from Dezhou,Dongying and Taian when the Cotton verticillium wilt was serious and we obtain202verticillium wilt strains2. Cultural characteristics were observed and201isolates were sclerotia-type which showed black colonies on PDA with white thin or thick aerial hypha, generating a large number of micro-sclerotia. Only1isolate formed white colony, cotton wool mycelium and no micro-sclerotia and melanin.3. PCR amplification on202isolates with specific primers DB19/DB22of Verticillium dahliae. Kleb, all isolates can amplified530bp bands around.This explains all isolates are Verticillium dahliae.4. Two pairs of specific primers (INTD2f/INTD2r and INTND2f/INTND2r) were used to amplify special regions for analyzing the distribution of defoliating type of V. dahliae in Shandong. The results show that201isolates can amplified about530bp specific bands with deciduous type primers INTD2f/INTD2r, accounting for99.5%of all isolates; only1isolate can amplified800bp bands around with non-deciduous type primer INTND2f/INTND2r, accounting for0.5%. It indicated the defoliating-type of V. dahliae was widely distributed in Shandong province., respectively, and202isolates5. The toxigenic capacity, wilting effect of toxin to cotton seed germination and cotton seedlings of8isolates have been analyzed. The toxigenic capacity of strain HDF4-3-1is the strongest, but toxin generation of3-5is weakest. It indicates the toxigenic ability of different strains is significant differences. Dealing with cotton seed and seedling with toxin, it show that the inhibition rate and wilt index of strain HDF5-3-1is the highest, strain HLX5-1-1is the lowest. The results indicated that virulence of selected strains is different.6. Antagonistic effect of the8biocontrol bacteria has been determined. Antibacterial radius of JK-14is maximum for24.0mm, strain A12is minimum for11.0mm. The results show that the antagonism effect is significant differences between strains. By16S rDNA identification, A12has been identifieded as Burkholderia pyrrocinia, The strain X-11, JK-14, SF-19, SF-23are belong to Bacillus spp, the strain JK-19, JK-28, JK-25are belong to Peanibacillus spp.