A Study Of Endophytic Bacteria On Colonization And Mechanism Against Phytophthora Capsici

To obtained endophytic bacteria against pepper Phytophthora blight well, this study isolated and screened endophytic bacteria against pepper Phytophthora blight from plants. Strains having great control effect were identified and determined their colonization in pepper, the relathionship between colonization and control effect, the effective number of bacteria which could be entirely against pepper Phytophthora blight. At the same time, mechanisms of biocontrol agents against pepper Phytophthora blight were determined, including the effect of their metabolites against Phytophthora capsici, Cellulase and β-1,3-glucanase activities, attenuating toxins of Phytophthora capsici in shoots and potted seedlings of pepper and induction of systemic resistance. Results are as follows:1 In this study, three strains(G9, R15 and J13)against pepper Phytophthora blight were obtained by plate dual culture and potted seedlings of control efficiency test from 172 endophytic bacteria isolated from eleven different cash crops and preservation 230 endogenous bacteria and their control effects were above 88.00%. G9, J13 and R15 were identified as different strains of Pseudomonasfluorescens II.2 Three strains could colonize in the pepper and all their colonization dynamics were in a ’first increased and then decreased’ trends. G9 and R15 colonized in the root and their maximum colonization amount were at 15d. J13 had the highest amount in roots, steems, leaves was 9d,15d and 15d and the colonization quantity was root> stem> leaf, when the colonization quantity of G9,J13 and R15 reached 9.73×105 cfu.g-1,10.31×105 cfu.g-1 and 6.30×105 cfu.g-1, their control effects were 100% and they could keep 100% control effect more than 6d,ld and 14 d.3 The biocontrol agents accessed pepper seedlings every 15d. R15 could complete a new cycle of colonization again and its colonization trend was the same all the time. Continuously repeated vaccination, R15 could maintain the colonization of 100% control effect in peppers,while G9 and J13 can’t.4 The extracellular products of G9, J13 have a weak effect on Phytophthora capsici, and the intracellular material of 3 strains were not against Phytophthora capsici.3 strains weren’t with cellulase, β-1,3-glucanase activity. The results of pepper Shoots test and potted seedlings trial suggested that 3 strains could not degrade or adsorption toxins of Phytophthora capsici.5 Although J13 could significantly induced CAT and POD activity increased in pepper, but the change trends of two kinds enzyme activity were not in conformity with the result of control effect, which suggested that the mechanism of J13 against pepper Phytophthora blight was not involved CAT and POD. G9 could significantly induce the SOD activity in vivo, and the change trend of SOD enzyme activity was in conformity with the result of control effect, which showed that the mechanism of G9 combating Phytophthora capsici may induce the SOD activity increased. Maybe G9 had other ways to confront pepper Phytophthora blight. R15 could not induce the CAT, SOD and POD in pepper. So the mechanisms of prevention and control of pepper Phytophthora blight of three biocontrol agents also needed to further explore.