Screening Of Antagonists From Pepper-Associated Bacteria For Biological Control Of Phytophthora Blight Of Pepper

In this study, more than 1500 pepper-associated bacteria, isolated from 4microenviroments (rhizosphere, phyllosphere, endorhiza and endosphere) were tested fortheir in vitro antagonistic activity against six phytopathogenic fungi (Phytophthora capsici,Pythium uItium, Fusarium oxysporum, Sclerotinia Sclerotiorum, Fusarium grarainearum,Botrytis cinema). Isolates with in vitro antagonistic activity against P. capsici were selectedto test their production of hydrolytic enzymes and siderophore. Antagonists, which stronglysuppressing P. capsici in vitro, were therefore genotypicaUy characterized by Amplified16S rRNA restriction analysis and assessed the best candidates for biological control. Thenantagonists were further assessed in greenhouse and the field experiment for controlphytophthora blight.In vitro antagonistic tests revealed that antagonist could most frequently found in thesebacteria isolated from endosphere, then from endorhiza, rhizosphere and phyllospher.Among 132 isolates of antagonizing P. capsici, 84 produced Cellulases or Proteases, 73produced Siderophores; but only 4 produce chitinase. At a cutoff level of 90%, antagonistscould be divided into 15 genotypic groups (G1-G15), 7 only consist of only 1 isolate, whilethe biggest one consists of 12 isolates.In the greenhouse, all 17 antagonistic isolates was found not only suppress the diseasecaused by P. capsici, but also promote the growth of pepper. According to the correlationcoefficient analysis, the greenhouse biocontrol efficiency was found positively correlatedwith in vitro antagonistic activity.In the field experiment, Bacillus cereus NJ02 was further evaluated for biologicalcontrol efficiency against Phytophthora blight with or without mancozeb. The resultsshowed that the relative control efficiencies of NJ02 and mancozeb were 75.81% and57.13% after 60 days treatment, respectively, but the relative control efficienciey was85.45% when NJ02 was inoculated after applied mancozeb 15 days. By culture communityof the rhizosphere soil on selecting medium showed that the NJ02, mancozeb and bothNJ02 and mancozeb had effect on fungi and bacilli communities, but not on actinomycete's.