Study On Biological Characteristics And Control Of Curvularia Clavata Pathogen Of Tobacco Leaf Spot

Leaf spot disease is one of the most important factors affecting the yield and quality of tobacco as a foliar economic crop.In recent years,the disease caused by the fungus of the genus Curvus sp.The leaf disease rate is as high as 30%,causing serious losses to tobacco production.In order to better control the Curvus sp.leaf spot disease,the pathogens were isolated from the collected samples of Curvus sp.leaf spot disease,characteristics,screening of effective agents and biocontrol bacteria,research on control effects,annd effects of chemical agents and biocontrol bacteria on phyllobacterial communities of tobacco plants susceptible to Curvus sp.leaf spot research content.The main research results are as follows:1.The pathogenic bacteria were isolated and purified from the disease samples collected from the tobacco-growing area of Zunyi City,Guizhou Province by conventional tissue isolation method.The pathogen of Curvularia clavata was identified as Curvularia clavata by morphological characteristics and ITS sequence phylogenetic analysis.Using Illumina and Nanopore nanopore sequencing technologies to sequence the genome of the pathogenic bacteria,the results show that the full-length mitochondrial genome sequence of C.clavata is 41763 bp,which includes 13protein-coding genes,2 r RNA and 23 t RNA,and the content ratio of 4 kinds of bases.It is close to the reported relative fungi,and has poor collinearity with the five relative species.Its genomes are very different,and the synonymous substitution rate of genes is greater than the non-synonymous substitution rate.All of them continue to evolve under purification selection.2.The biological characteristics of pathogenic bacteria were determined by the method of mycelial growth rate.The results showed that the optimum temperature for the growth of pathogenic bacteria was 28℃,the optimum p H range was 6-9,and the growth rate was the fastest on Oat Agar medium.When soluble starch was used as carbon source and beef dipping powder was used as nitrogen source,it was the most favorable for mycelial growth;the lethal temperature of mycelium was 53℃for 10 min,and there was no significant difference in light conditions on mycelial growth.3.The indoor virulence of 13 agents against pathogenic bacteria was determined,and 2antagonistic bacteria with strong inhibitory effect on pathogenic bacteria were screened out,and the field control efficacy was determined by foliar spraying.The results showed that in the indoor toxicity test,prochloraz aqueous emulsion had the strongest toxicity,and the EC₅₀ value was the smallest,which was only 0.2297μg/m L,followed by epoxiconazole suspension,whose EC₅₀value was 0.4054μg/m L.Two strains,YC2102 and YC3049,were screened from the 85 tested biocontrol bacteria,which had strong antagonistic effects on the tested pathogens.Among them,YC2102 was a biocontrol bacteria,and YC3049 was a biocontrol actinomycete,and the antibacterial rates were 75.76%and 68.53%,After identification,YC2102 is Burkholderia contaminans,and YC3049 is Streptomyces olivaceus.The field control effect test showed that the control effects of prochloraz and epoxiconazole were the best,with the control effects being64.66%and 59.49%,respectively,which were significantly higher than the control effects of other chemical treatments.the preferred agent.The secondary metabolites produced by B.contaminans and S.olivaceus can promote plant growth and inhibit the growth of pathogenic bacteria,and have the potential to be developed as biocontrol agents.4.High-throughput sequencing technology was used to analyze the composition of phyllosphere bacterial community before and after the onset of Curvus sp.leaf spot disease,infection by a single pathogen,infection by multiple pathogens,and treatment with chemicals and biocontrol solutions.The results showed that after different types of pathogens infect the tobacco plants,the dominant genus of phyllosphere bacteria were different,and the dominant genus was screened by the pathogen C.clavata as Pseudomonadales.The phyllosphere bacterial community richness index increased first and then decreased after the chemical agent and biocontrol bacterial solution treatment.After the chemical agent prochloraz and YC2102 treatment,the relative abundance of beneficial microorganism Stenotrophomonas increased significantly,while the control and YC3049 treated the relative abundance of Stenotrophomonas.The relative abundance of Pseudomonas was significantly decreased,but the relative abundance of Pseudomonas increased significantly compared with other treatments.The bacterial communities of each treatment and the control group were significantly different,and the treatments of chemical and biocontrol bacteria significantly changed the phyllosphere microbial community diversity.