Research Of Pathogenicity,Drug Resistance And Genetic Diversity Of Pythium Vexans

Ramie is an important economic crop,which plays an important role in textile,military and medical fields.In addition,ramie also plays an important regulatory role in the ecological control of soil and water loss,and its role in ecological aspects also stabilizes the ability of sustainable development of the natural environment,which is closely related to human life.In 2013,a new disease named"root brown rot"was found in the main production areas of ramie in China,which caused serious damage to the main production areas and seriously affected its high yield.Pythium vexans is the main pathogen of root brown rot of ramie.In order to control the root brown rot prevalent in the main producing areas of ramie in China,samples of diseased roots were collected from Hunan,Hubei,Sichuan,Chongqing and Jiangxi.The pathogenicity,drug resistance and population genetic relationship of the pathogen group were studied to deeply understand the ramie root brown rot pathogen and comprehensively understand the control object of ramie root brown rot disease,so as to provide reference and theoretical basis for the field control of ramie root brown rot disease in the future.1.The difference of pathogenicity of Pythium vexans causing brown rot of ramie in different areas was investigated by indoor greenhouse culture method.66 strains of ramie diseased roots were isolated and identified in 5 main producing areas,and 10 strains were selected for pathogenicity identification.The results of pathogenicity identification showed that all 10 Pythium vexans strains had pathogenicity,and YC2-1a and RCLJ5-1 had strong pathogenicity.According to the disease index of each strain,the pathogenicity of different strains to ramie was obviously differentiated.The results of cluster analysis showed that the virulence of strains from different main producing areas was different,which could be divided into forced virulence?20%?,moderate pathogenicity?20%?and weak pathogenicity?60%?.At the same time,it can be seen from the cluster analysis group that the virulence of the strains has no correlation with geographical origin.2.18 kinds of high-efficiency and low toxicity fungicides commonly used in the market were selected,and the fungicides with good antibacterial effect against Pythium vexans were screened out by the method of containing toxic medium.The EC₅₀ of fungicides with good antibacterial effect was determined to determine the germicidal efficacy of the selected fungicides on Pythium vexans.The results showed that five kinds of fungicides have good control effect,namely metalaxyl mancozeb,mancozeb,captan,bromothalonil and SYP-Z048,and the inhibition rate reached 100%.Among them,metalaxyl mancozeb was the best,and its EC₅₀ was 1.004 mg/L.Benomyl,Bacillus subtilis and Trichoderma harzianum had little effect no P.vexans HF1.Moreover,metalaxyl mancozeb mentioned-above with the best effect on P.vexans were used to measured their toxicities on isolates from different regions.The results showed that there was no significant difference in fungicides resistance between the isolates in different regions.3.Eight typical and highly different strains were selected from five main ramie producing areas in China.SSR-PCR amplification and capillary electrophoresis were used by Gene mapper 4.1 through data analysis,six pairs of primers with high specificity and good polymorphism were screened out from50 pairs of primers from pvg1 to pvg50,which were PVG3,PVG10,PVG22,PVG24,PVG33 and PVG36.Six pairs of primers were used to amplify 66 Pythium vexans strains by SSR-PCR.Ntsyspc2.1and POPGENE32 software were used for data processing and UPGAM method was used for cluster analysis.The results showed that the number of alleles amplified by each pair of SSR primers was 7?19,with an average of 12;the number of effective alleles was 3.1983?6.8035,with an average of 5.2303;at the population level,the gene diversity index?Gd?was 0.6987?0.8530,with an average of 0.7958;Shannon information index?I?was 1.5022?2.3016,with an average of 1.9184;PIC polymorphism information content was 0.6689-0.8400,with an average of 7729.The results of cluster analysis showed that 66 strains could be divided into group I and group II when the genetic similarity coefficient was0.84,and there were three groups under each cluster group.The strains from the same geographical origin basically gathered together,and there was a certain correlation between genetic distance and geographical origin of Pythium vexans.