The Biocontrol Mechanism Of Ginkgo Biloba Endophytic Bacterial Strains To Pepper Phytophthora Blight

Three endophytic bacterial strains, Hy7, Z2-13and Gbl8(Bacillusamyloliquefaciens), isolated from Ginkgo biloba leaves collected in different regionswere screened to control phytophthora blight of pepper fruit. The control effect of asingle strain reached to60%in6d after inoculating with Phytophthora capsici.Further experiment indicated that it was significantly effective for Hy7and Z2-13tocontrol phytophthora blight of pepper seedlings in greenhouse and the control effectreached to60.76%and50.71%in10d after inoculating with the pathogen respectively.The different strains were mixed and used to control the same disease. The resultsindicted that the mixture of Z2-13and Hy7had better control effect contrasting to asingle strain. The effect of mixture reached to83.33%in4d and remained at57.78%in8d after inoculating with the pathogen on pepper fruit. The effect of the mixturereached to79.56%in6d after inoculating pepper seedlings with P.capsici, andremained60.0%in10d. These results showed the biocontrol effect of mixed strainswas more durable and stable than that of a single strain.The biocontrol mechanism was preliminarily researched from three aspects:colonization ability, antagonist action of metabolites and induced disease resistance.To confer colonization ability, the endophytic bacteria were constructed with gfp.Both strains, Z2-13and Hy7, could colonize in the pepper seedling, and thepopulation reached to2.00×104cfu/(g.fw). Labeled-gfp strains could be isolated frompepper seedlings after30days of colonization. Labeled-gfp strains transmitted interpepper tissues, and the population density of Hy7in roots was more than that in aerialparts. The colonization count of Hy7was higher than Z2-13. The bacterialcolonization number of mixture of Hy7and Z2-13was similar to a single strain. Thismight be related to limited living sites of the plant. The changes of various defensiveenzyme activity produced by the pepper seedling after inoculating with endophyticbacteria showed that Hy7induced more disease resistance expression in comparisonwith the strain Z2-13. The activities of CAT, POD, SOD and PAL of the pepperseedling treated with the mixed strains were higher than that of the control. However,the activity of CAT and PAL elevated observably after inoculating with endophyticstrains and challenged P.capsici. The PCR amplification results showed the strainZ2-13and Hy7carrying the gene family determining the lipidpeptide synthesis. Thelipidpeptides extracted from metabolites could induce alternation on hyphaemorphology and reduce the sporangia production of P.capsici, and inhibit the hyphae growth of some pathogenic fungi simultaneously. The results showed that it was ofwidely biocontrol potential for strains Z2-13and Hy7.It was more efficient against pepper phytophthora blight when the plants weretreated by the mixture of the endophytic bacteria. But different strains had differentcontrol mechanism. The metabolite of the strain Z2-13played a significant role on itscontrol effect, but the strain Hy7played by inducing system resistance.