Screening, Identification And Evaluation Of Bacteria Strains Against Fusarium Wilt Of Watermelon And Their Antagonistic Mechanism

Fusarium wilt of watermelon is one of the main diseases on watermelon.which affects the watermelon yield seriously. Based on production practice of watermelon, this paper isolated, screened the effective antagonistic strains against Fusarium oxysporum f. sp. niveum from the rhizosphere soil and the roots of watermelon, cucumber, and eggplant, then classified and identified two strains. The inhibiting effective on pathogens and the colonization ability on watermelon by antagonistic strains were assayed in greenhouse and the field, furthermore, We studied the mechanism of antagonism. And expected it could provide theoretical foundation and reference. The main results were as follows:(1)1050bacterial strains were isolated from the rhizosphere soil and the roots of watermelon,cucumber, and eggplant in Neimenggu, Xinjiang, Anhui, Henan, Jiangsu and Jiangxi province. Among the tested strains,9strains could inhibit the mycelia growth of Fusarium oxysporum f. sp. niveum, Alternaria brassicicola, Phytophthora capsici and Botrytis cinerea. Two strains, NBT-15and PL-82, had strong inhibitrry activity against F. oxysporum in vitro, with the inhibition rate of60.5%and55.3%, respectively.(2) Based on the result of the inhibition rate in vitro,9strains were chosed to test in the greenhouse,all9antagonistic isolates were found not only suppress the disease caused by F. oxysporum,but also promoted the growth of watermelon. The result of pot experiment against F. oxysporum indicated control effects of NBT-15and PL-82were80.4%å'Œ75.6%after30days’treatment,better than other7strains. The result of field trial demonstrated that the control effects of NBT-15and PL-82were70.05%and50.43%,better than NBT-15, respectively.(3) The abilities of NBT-15and PL-82producing cell-wall-degrading enzymes (chitinase, proteinase and cellulase), siderophore were researched. The result showed that NBT-15could produce cellulose, siderophore and lectins, and the PL-82could produce cellulase, siderophore, but they were not the producer of chitinase, which suggested that NBT-15and PL-82had antibiotic activity against phytopathogenic fungi because of the producing of proteinase, cellulose, siderophore and lectins. Certainly, it was also possible that other antibiotic materials could play a role in antibiosis. Colonizing of NBT-15isolated marked with Rifampicin on the soil and rhizosphere of watermelon were investigated. The results showed that NBT-15could be colonized in soil. Population of NBT-15isolated declined with prolonging time and received0after treatment27days,the control effect would be better when you watered the root on the15th day.(4) Based on their morphology, physiological, biochemical characteristics and16S rDNA sequence analysis, the strains NBT-15and p1-82were identified to be Bacillus subtilis and Pseudomonas aeruginosa, with GenBank accession number HQ244501and HQ259594,respectively.