Study On The Biocontrol Effect And Growth Promotion Of Bacillus Velezensis J-4 On Peach Root Rot

Peach root rot is a typical soil-borne disease caused by a variety of pathogenic fungi,which seriously affects the yield and quality of peaches and causes huge economic losses.Peach growers rely on chemical control all the year round,which is extremely harmful to the health of consumers and the environment.Biological control treatment is considered a friendly and feasible alternative.In this study,the pathogen of peach root rot in Sihong county,Jiangsu province was isolated and identified.At the same time,the pathogen was used as the target fungus to screen the biocontrol bacillus,and the biocontrol bacterium J-4 with the best antibacterial effect was systematically identified.Pot experiment was carried out and the disease resistance and growth-promoting effects of J-4 strain were verified.Finally,the functional strain J-4 was optimized for medium composition and fermentation conditions,laying a foundation for the next development of special functional bio-organic fertilizers.The main research results were as follows:(1)10 fungi were screened out by in-situ screening method from soil samples in Sihong,Jiangsu Province.After pathogenicity verification,a peach tree root rot pathogen G-1 was identified,and the strain was systematically identified.It was clear that the main pathogen of peach root rot in the peach orchard in Sihong country,Jiangsu province was mainly Fusarium solani.(2)56 isolates of Bacillus were obtained from the rhizosphere soil samples of peach trees.With the pathogenic Fusarium solani G-1 as the target fungus,8 strains of Bacillus with antagonistic effect were obtained through preliminary screening,and the results were confirmed by re-screening.A strain of Bacillus J-4 with the best antagonistic effect was systematically identified as Bacillus velezensis through morphological observation,physiological and biochemical determination,as well as molecular biology analyses.(3)The pepper plants with the same pathogens,short growth cycle and quick effect were selected as the alternative research objects,and the pot experiment of the root rot biocontrol effect was carried out.In the pot experiment,the biocontrol effect of the fermentation broth of the biocontrol bacterium B.velezensis J-4 against root rot pathogen reached 58.06%.At the same time,the plant height,root length,fresh weight,dry weight,chlorophyll content and other biological indicators increased significantly,comparing to the control.Therefore,the test strain had good disease resistance and growth-promoting effects.(4)The single factor optimization experiment was used to optimize the medium composition and fermentation conditions of the biocontrol bacterium B.velezensis J-4.The results showed that the best medium composition of B.velezensis J-4 was 3%corn meal,1%yeast extract,0.5%Na Cl;the best fermentation conditions were 36°C,p H 5.68(natural),fermentation time 24 h,inoculation amount 1.5%.The three significant factors that affect bacterial fermentation were selected by Plackett-Burman test:yeast extract,temperature,and fermentation time.The optimal value obtained by response surface test was yeast extract 0.96%,temperature 35.86℃,fermentation time 24.15 h.It was predicted that the amount of fermented bacterium was as high as 3.64×10~9CFU/m L,and the highest number of viable bacterium was 3.52×10~9CFU/m L in the following verification test.