Biocontrol Effect And Rhizosphere Colonization Characteristics Of Paenibacillus Polymyxa P8-1

Pepper blight is a typical soil-borne disease.The plant will wither and die as soon as the disease occurs.It is difficult to recoverand and it seriously affects the yield and quality of pepper.In this study,rhizosphere bacteria wereisolated from different plant root soilsand and biocontrol bacteria with antagonistic effect against Phytophthora capsici were screened.Through thedetection of its inhibitory activity and control effect against Phytophthora capsici,the colonization ability,the influencing factors of growthpromoting effect and its influence on rhizosphere soil microecology,they could provide biological control resources and theoretical basis for the biological control of Pepper blight.In this study,bio-control bacteria P8-1 was isolated and identified as Paenibacillus polymyxa based on its culture characteristics,physiological and biochemical characteristics and 16S rDNA sequence analysis.P8-1 strain could significantly inhibit the growth of hyphae,formation of zoosporangium,release of zoospores and germination of stasis spore of P.capsici,and the inhibition effect on the germination of stasis spore reached 100%.In pot experiment,the control effect of P8-1 strain on pepper blight reached 71.44%.P8-1 also increased the activities of phenylalanine ammonia-lyase,polyphenol oxidase,catalase,chitinase andβ-1,3-glucanasein pepper leaves.The resistance of pepper leaves to pepper blight when P8-1 infused into the root of pepper.In the field experiment,P8-1 could promote the growth of pepper and regulate the soil microecology.Bio-control bacteria P8-1 also could significantly increase the chlorophyll content and the root activity,as well as the contents of protein,vitamin C and soluble sugar in pepper fruits,and increased pepper production.At the same time,P8-1 significantly increased the rooted soil enzyme activity and the content of available nitrogen and phosphorus,increasedthe number of rhizosphere bacteria and actinomycetes,reduced the number of fungi,which significantly increased the abundance of fibrobacteria,actinomycetes,blastomonas and verrucobacteria in pepper rhizosphere soil,and reduced the abundance of potentially pathogenic bacteria.P8-1 strain had wellcolonization ability in the rhizosphere of pepper.The colonization density of P8-1 in root tip was 2.31 ×103 cfu·cm-1 measured by double-layered filterpaper method in dish,and the colonization density of P8-1 in root was more than 103 cfu·g-1 measuredin pot experiment,up to 104 cfu·g-1.The root exudates of pepper,Phytophthora capsici and indigenous microorganismson can significantly affect colonization ability of P8-1 in pepper.Effects of Phytophthora capsiciin peppercan improve the colonization of P8-1,through the vaccinated and unvaccinated Phytophthora capsici two processing capsicum root secretion of primary metabolites,vaccinated Phytophthora capsicican significantly improve content of amino acids in root exudates of L-arginine,L-leucine and L-tryptophan.P8-1 strain can form a biofilm.It has obvious chemotaxis to amino acid such as arginine,leucine,isoleucine,tryptophanand so on.Exogenous amino acids such as arginine,leucine and tryptophan promoted the colonization of P8-1 in the rhizosphere of pepper.