Pathogen Identification And Biocontrol Strain Screening Of Tobacco Target Spot Disease In Hunan

Tobacco target spot disease has been prevalent in some tobacco areas of Hunan in recent years,which is caused by Rhizoctonia solani.Once the disease occurs,it spreads rapidly and causes great economic losses to tobacco farmers.In this study,tobacco target spot samples from Hunan tobacco-growing areas were collected for pathogen isolation and molecular identification.Their pathogenicity was determined,and their fusion groups were analyzed.Two antagonistic bacteria with biocontrol effect against Rhizoctonia solani were screened from tobacco rhizosphere soil.The results are as follows :(1)Tobacco target spot disease diseased leaves were collected from Yongshun County,Cili County,Longshan County,Shimen County and Zhangjiajie City in Hunan Province,and 13 pathogenic bacteria were isolated and purified from the diseased leaves by tissue separation method,and verified by Koch’s rule.After molecular testing,a phylogenetic tree was constructed and the pathogen was determined to be Rhizoctonia solani Kühn.The 13 isolated R.solani fusion clusters were determined by the confrontation culture method,and the 13 R.solani strains were determined to belong to The four fusion subgroups of the fusion group AG-3,of which 5 strains isolated from Yongshun are judged to belong to one fusion group;LS1,ZJJ and SM belong to the same fusion subgroup;LS2,CL1-1 and CL1-2 belong to the same fusion group A fusion subgroup;CL2-1 and CL2-2 belong to the same fusion subgroup.(2)13 strains of R.solani were inoculated on tobacco leaves,and the pathogenicity of strain YS1 was the strongest,and SM was the weakest.The highest incidence of YS1 was 76.67 %,and the lowest incidence of SM was 36.67 %.The average lesion diameter(AD)of YS1 infected tobacco leaves was 12.08 cm,and the pathogenicity was the strongest.The SM AD value was 1.97 cm,and the pathogenicity was the weakest.The disease index of tobacco leaves inoculated with YS1 was the highest(72.22),and the disease index of tobacco leaves inoculated with SM was the lowest(13.70).The study of cross pathogenicity showed that maize sheath blight could infect tobacco,but tobacco target spot could not infect maize.Rice sheath blight can not infect tobacco and tobacco target spot can not infect rice.(3)Two antagonistic bacteria GT-5 and GT-6 against tobacco leaf spot were screened from rhizosphere soil of tobacco.They had significant inhibitory effects on the mycelial growth of tobacco leaf spot pathogen.The inhibitory rate of strain GT-5against tobacco leaf spot pathogen was 63.98 %,and that of strain GT-6 was 50.07 %.Molecular identification showed that GT-5 was Bacillus amyloliquefaciens and GT-6was Pseudomonas aeruginosa.