Research Of Bacterial Isolate For Biocontrolling Rubber Tree Powdery Mildew

276bacterial strains were separated from rhizosphere soil of rubber tree plantation. And two of them (S43and S55) have obvious antagonism against rubber tree Powdery Mildew. Based on the analysis of morphologic observation, cultural characteristics, physiological and biochemical properties, and the sequential analysis of16S rDNA, S43strain and S55were identified as Bacillus subtilis.By means of Oidium heveae Steinm's spore test and potted seedlings experiment, the results showed that the inhibition rate to the spore germination and control effect were improved with the increasing of the concentration of fermented filtrates.20%of fermentation filtrates of strain S43and S55had effective inhibition activity against powdery mildew spores germination, with the inhibition rate of80%. Meanwhile, the control effect of the pot experiment also reached80%. This showed that the fermentation filtrates of strain S43and S55had good prevention effect to powdery mildew.Spraying fermentation filtrates or bacterial suspension24h beforen48h after or while with powdery mildew inoculation. PPO, POD activity in the Rubber tree leaves inoculated with strain S43and S55had nearly doubled compared with the control, indicating that the strain S43and S55can induce the production of defence enzyme in plant. The control effect of S43fermented filtrates with three kinds of inoculation treatments were84.62%,76.53%and43.32%respectively as well as the inhibition rates were57.32%,56.56%and21.02%respectively with bacteria suspension of which the control effect was poorer. With the same methods of S55, the inhibition rates were82.35%,80.57%and57.94%respectively as well as the inhibition rates were57.76%,57.74%and32.29%respectively with bacteria suspension of which the control effect was poorer. The results were as follows:1. spraying24h before or while inoculation, the inhibition rate had obviously higher than that of48h after inoculation;2. fermentation filtrates had better control effect than that of bacterial suspension;3. compared with S55, fermentation filtrates of S43had better control effect to powdery mildew.Colonization of marked strain S43and S55was researched in Rubber tree by inoculation with injuring leaves and no injuring leaves. The results showed that the marked strain S43*and S55*could set the largest colonization in the rubber leaves on the first day after inoculation. While as time went on, the population of setting reduced gradually and the population of the marked strain was almost stable after15days. The population of marked strain by treatment with injuring leaves was twice than that of with no injuring leaves at the early inoculation, but the amount of colonization of the marked strain showed no significant difference at last.The preliminary optimizing conditions for the antagonistic strain S43were as follows:the optimal medium:sucrose1.5%, peptone0.67%and yeast exact0.33%; the fermentation conditions:temperature30℃, pH7.0, rotation speed150r/min; inoculation amount2%, medium and air ratio2:5, the best inoculation age of strain14-3Oh and the optimum fermentation time36--72h.