Screening And Identification Of Biocontrol Bacteria Against Sweet Potato Black Spot And Effect Of Disease Control And Growth Promotion

Sweet potato is one of the important economic crops in my country and has high nutritional value.Sweet potato black spot is a soil-borne disease caused by Ceratocystis fimbriata Ellis.et Halsted,which seriously affects the development of sweet potato industry.Biological control has the characteristics of environmental friendliness and low cost,and is an effective way to control sweet potato black spot.In this study,the strains with antagonistic effect on the sweet potato rhizosphere were screened from the sweet potato rhizosphere soil,and their growthpromoting function was identified.The whole genome sequencing of the strains with good antagonistic effect was carried out to analyze the antagonistic mechanism,and the pot experiment was used to verify the disease prevention of antagonistic bacteria.Growthpromoting effect,the main research results are as follows.(1)Five strains with better antagonistic effects were screened from sweet potato rhizosphere soil,and all five strains had multiple growth-promoting functions.Through morphological observation,identification of physiological and biochemical characteristics,and16 S r RNA gene analysis,the five strains were identified as Bacillus halotolerans B13,Bacillus siamensis C19,Bacillus velezensis B1,Bacillus wiedmannii A6,Bacillus subtilis B11.(2)Whole genome sequencing was carried out on strain B13 with good antagonistic effect.The genome of strain B13 was composed of a chromosome and a plasmid,both of which were circular.The GC content is 35.41%.The secondary metabolic gene clusters in the B13 genome were predicted,and a total of 10 secondary metabolic gene clusters were predicted,and 5 gene clusters were 100% similar to the gene clusters reported by previous researchers.The key genes related to antibiotic production in the B13 genome were analyzed,and a total of 6 key genes of antibiotics were retrieved,among which,the key genes for the synthesis of Surfactin include srf AA,srf AB,and srf AC;the key genes for the synthesis of Bacillaene include 10 genes such as fab D;The key genes for the synthesis of Fengycin include 7 genes such as fen A,fen B,fen C,fen D,fen E,and lde G;the key genes for the synthesis of Bacillibactin include 3 genes including dhbc;the key genes for the synthesis of Subtilosin A include sbo A and alb A;the key genes for the synthesis of Bacilysin is O0R52＿19665.(3)The results of pot experiment showed that the control effect of different treatment groups on sweet potato black spot was 43.75%-84.38%,and the control effect of B.halotolerans treatment group T1 on sweet potato black spot was the best,which was 84.38%.At 60 days,compared with the control group,the growth value of main vines in the bacterial agent treatment group increased by 4.99%-123.13%,the growth value of stem diameter increased by 29.64%-128.85%,and the leaf peroxidase increased by 3.41%-70.45%,catalase increased by 18.52%-240.74%,superoxide dismutase increased by 6.17%-18.23%,malondialdehyde decreased by13.39%-40.37%,and the relative content of chlorophyll increased by 0.55%-3.71%.At 120 days,compared with the control group,the fresh weight of the shoots in the bacterial treatment group increased by 4.68%-39.94%,the dry weight of the shoots increased by 9.87%-49.36%,the fresh weight of the roots increased by 5.24%-118.78%,and the dry weight of the roots increased by 5.24%-118.78%.Weight increased by 4.40%-119.45%,soil catalase increased by3.45%-13.79%,sucrase increased by 5.28%-24.02%,phosphatase increased by 18.57%-43.77%,urease increased by 6.17%-20.80%,the organic matter increased by 1.03%-11.34%,the alkaline nitrogen increased by 2.55%-10.40%,the available phosphorus increased by4.45%-13.77%,the available potassium increased by 0.75%-26.55%,and the soluble protein content of sweet potato roots increased by 1.41%-22.86%,the soluble sugar content increased by 4.35%-73.38%,and the total starch content increased by 7.40%-35.57%.The results of principal component analysis showed that the growth-promoting effect of B.halotolerans group T1 on sweet potato was the best.In summary,the application of bacterial agents has a certain control effect on sweet potato black spot,and can also promote sweet potato growth,improve agronomic traits,enhance leaf antioxidant enzyme activity,improve sweet potato stress tolerance,and improve sweet potato rhizosphere soil enzyme activities and nutrients.content and improve the nutritional quality of sweet potato.This study provides strain resources for the control of sweet potato black spot and provides a theoretical basis for the construction of high-efficiency biocontrol fungicides.