Screening And Identification Of Microorganisms Against Phytophthora Sojae And Their Antagonistic Activity

Phytophthora sojae is one of the very important plant pathogenic organisms inagricultural production. Soyben Phytophthora blight caused by the oomycete is adestructive disease of soybean in the world. Screening of potential antagonistic bacteriaagainst Phytophthora sojae will be helpful for finding new targets of chemical controland providing good ideas for designing new control strategies. Based on the screeningmicroorganisms against Phytophthora sojae, the identification of strain BY-2and BZ-2and their antagonistic activities to P. sojae were carried out in this paper. The mainresults were as follows:1. By using agar-plate dual culture and the cup plate method, the inhibitory activititiesof the six Trichothecium roseum strains and Trichoderma harziarum strain TH-1andBacillus subtilis strain BS kept in our laboratory were investigated respectively, and theresults showed that the inhibitory effects of these isolates were all not significant against P.sojae.2. Four antagonistic bacterial strains were obtained by collecting and isolating fromthe rhizosphere soil of growing soybean in the diseased fiels of Anhui province. In theplate dual-culture test, the two bacterial isolates, BY-2and BZ-2, among them showedstrong antagonistic activities against P. sojae, with the inhibitory effects of79.00%and63.97%,when five days, respectively. Therefore, the identification of BY-2and BZ-2wasdone, respectively. Based on morphological test, the morphological and physiological andbiochemical analyses, observation by electron microscope and phylogenetic analysis of16S rDNAand gyrB sequences, the two strains were all identified as Bacillus subtilis.3. The inhibitory activities of different-time metabolic liguid of strain BY-2against P.sojae were tested. The results showed that the inhibitory effect of72h metabolic liguid onmycelial growth was the highest, with the inhibitory effect of40.93%; the inhibitory effectof72h metabolic liquid of BY-2to P. sojae AH19isolate was significant higher than thatof all other strains. The results also showed that BY-272h metabolic filtrate couldsignificantly inhibit the germination of zoospores and.the inhibitory effect of BY-2was upto57.71%at24h after treating with the metabolic filtrate, which was significantly higherthan that of the other treatments.4. The inhibitory activity of volatiles from BY-2against P. sojae was tested bymeans of dish-buttoning method. The results showed that the volatiles of BY-2canstrongly inhibit mycelium growth of tested isolates in P. sojae. However, the inhibitory rates of volatiles were significantly different with different P. sojae isolates and differenttreatment time. And the inhibition rate against AH19at7d after treatment was the highest,reaching91.94%.5. The potted experiment was carried out to examine the in vivo control effectivenessand growth-promotion of the biocontrol strains obtained by screening experiments. Theresults showed that the control effectiveness of strain BY-2to the disease by applying rootdipping with the bacterial liquid3days prior to inoculation was significantly higher thanthat of theother treatments, and the control effectiveness was75.01%at10d afterinoculation. At the same time, the bacterium fluid of BY-2could promote the soybeangrowth significantly. Compared with the control，the fresh weight and the dry weightincreased by63.16%and43.48%, and the roots length and the stems length increased by56.57%and6.95%, respectively.6. The influences of temperature, pH, inoculum dosage and culture time on strainBY-2were studied. The results indicated that the the optimum temperature was30℃, theoptimum pH was7.0, the optimum inoculum dosage was2%and the optimumculture timewas48hours.Under these conditions the strain could grow better and gain the highestantifungus activity. This would provide the basis for the next development of biocontrolagents from strain BY-2.