Isolation And Functional Study Of Endophytic Bacteria From The Placenta Of Pepper Fruit

Capsaicin is the main component of pepper fruit.The placentation of pepper fruit is not only the location of seed,but also the main location of capsaicin synthesis and storage in all tissues of pepper plant.Capsaicin and its metabolites have a variety of biological activities,such as in the food industry as additives,in the pharmaceutical industry as antibacterial,antitumor and analgesic drugs and widely used.Therefore,isolation of biocontrol bacteria from the placentation of pepper fruit may be helpful to the colonization of the postnatal biocontrol strains in the placentation,and through the placenta into the seed and passed on to the next generation,so as to improve the biocontrol effect.Based on the above hypothesis,this paper preliminarily determined the most suitable isolation medium by comparing the isolation efficiency of different medium for endophytic bacteria in placenta of pepper fruit,and screened the biocontrol strains against sclerotium rolfsii Sacc、Phytophthora capsici and Colletotrichum capsici through confrontation culture,then evaluated the ability of different strains to degrade capsaicin,and finally compared the biocontrol effect of biocontrol strains on sclerotium rolfsii Sacc by pot experiment。The specific research results are as follows:1.In this paper,the method of dilution coating was used to separate endophytes from the placentation of pepper fruit.The culture medium of R2A,PDA,NA,nutrient agar,pepper leaf,pepper root,pepper fruit placentation and pepper root soil were used to determine the most suitable culture medium for the growth of endophytes in the placentation of pepper fruit.According to the analysis of variance,the number of endophytes isolated from the pepper fruit placentation placentation medium was the highest,and the number of endophytes isolated from the PDA medium and the pepper root soil medium was the highest.2.Strains with good antagonistic effect were isolated from the endophytic bacteria of pepper fruit placenta,and their ability of capsaicin degradation was further investigated,and antagonistic bacteria with better ability of capsaicin degradation were screened out.Antagonistic bacteria with antagonistic effect on sclerotium rolfsii Sacc.Were isolated from the placentation of pepper fruit.The results showed that 17 strains had antagonistic effect on sclerotium rolfsii Sacc.Six antagonistic strains G242,T443,YZ12,G241,T151 and T442were also found to have bacteriostatic effects on the pathogens of Phytophthora capsici and Colletotrichum capsici,with the relative inhibition rate reaching over 48%.The results of16S rRNA identification showed that strains G242 and T443 were Bacillus velezensis,strains YZ12、G241、T151 and T442were B.amyloliquefaciens.Strains which can degrade capsaicin were isolated from the endogenetic antagonistic resources of pepper fruit placenta.Eleven antagonistic strains were found to have more than 25%degradation efficiency by HPLC.Among them,the degradation efficiency of strains T222,TZ53 and YZ12 reached 97.17%,96.13%and 89.73%respectively.The degradation products of capsaicin degraded by strain TZ53 were separated and purified by preparative liquid chromatography.The molecular formula of degradation products 1 and 2 were C₁₇H₂₇NO₄,which were isomers of each other.3.Strains G241 and T443 were selected for pot experiment to compare the control effect of each strain on Sclerotium rolfsii Sacc.The results of pot experiment showed that the inhibition effect of compound biocontrol strains was significantly higher than that of single strain.The control effect of G241 and T443 was 88.41%,higher than that of G241（29.14%）and T443（38.16%）.