Study On Genetic Diversity Analysis Of Pathogen And Chemical Control Of Tobacco Brown Spot In Jiangxi Province

Tobacco is an important commercial crop in Jiangxi Province,with an annual planting area of more than 15000 hm~2,which has created considerable economic benefits for tobacco farmers.With the development of tobacco planting industry,the occurrence and harm of tobacco brown spot disease in Jiangxi Province have been increasing in recent years,causing huge economic losses to the tobacco industry.In this paper,the species of the pathogen of tobacco brown spot disease in the main tobacco areas of Jiangxi Province were identified,and the genetic diversity of the pathogen was analyzed.At the same time,the indoor toxicity test and field efficacy test of the fungicides were also carried out to screen out new fungicides to control tobacco brown spot disease.The main results were as follows:In 2021,forty-seven strains of Alternaria sp were isolated and purified from fifty-nine samples of tobacco brown spot disease collected from six major tobacco areas in Jiangxi Province.Through morphological and molecular biological identification,forty-seven strains of pathogenic bacteria can be divided into two major groups:Alternaria alternata and A.tenuissim.Thirty-seven strains are A.alternata,accounting for 78.7%;Ten strains are A.tenuissim,accounting for 21.3%.A.alternata is the dominant specie of tobacco brown spot in the main tobacco areas of Jiangxi Province.The genetic diversity of thirty-seven strains of A.alternata from six major tobacco areas in Jiangxi Province was studied by RAPD molecular marker technology.The results showed that the Nei,s diversity index(He)of different geographical sources was 0.1618～0.3209,and the Shannon’s information index(I)was 0.2419～0.4785,indicating that the genetic diversity of A.alternata strains from different geographical sources was rich,and the level of genetic diversity among populations from different geographical sources was different.The genetic differentiation coefficient of populations from different geographical sources is 0.2518,the average genetic distance is 0.1160,the average genetic similarity is 0.8909,and the migration number per generation(Nm)is 1.8171.Xingguo County and Xinfeng County have the smallest genetic distance and the largest genetic similarity;Shicheng County and Lichuan County have the largest genetic distance and the smallest genetic similarity,indicating that there are different degrees of gene exchange among the six geographical populations,but the degree of genetic differentiation is not significant.When the similarity coefficient is 0.56,the UPGMA system clustering of thirty-seven strains can divide the strains into Ten groups,and the thirty-seven strains are basically clustered to the corresponding branches based on the geographical origin,indicating that the genetic diversity between strains has obvious correlation with their geographical origin.Through the mycelial growth rate method and spore germination method,the indoor toxicity of thirteen fungicides was determined,and seven fungicides with good inhibition effect were selected for field efficacy test.The test results showed that 30%pyrazolin·tebuconazole SC,40%haloperidine·isocarbazon SC,48%difenoconazole·azoxystrobin WP were the best fungicides for the control of tobacco brown spot disease,and were recommended as alternate fungicides for the control of tobacco brown spot disease.