Isolation And Identification Of Antagonistic Bacteria Against Fusarium Oxysporum F. Sp. Momordicae And Study On Its Potential Of Biocontrol

Bitter gourd wilt is a soil-borne disease caused by Fusarium oxysporum f.sp.momordicae and tremendous yield losses has been caused in production of bitter gourd in the worldwide.Shandong province is one of the major production region of bitter gourd cultured in greenhouse in the northern areas of China.Because of continuous monoculturing,the occurrence of bitter gourd wilt is increasing and become a seriously limiting factor of good quality and high yield of bitter gourd in Shandong province.In order to learn about the occurrence of bitter gourd wilt and screening of the antagonistic strains of bitter gourd wilt,those samples collected from field area with serious bitter gourd wilt in Shouguang and Feicheng of Shandong province have been preliminary investigated for isolation and purification of pathogenic fungus and antagonistic bacteria,pathogenicity test of fungal isolates,antifungal activity of bacterial isolates,morphological identification of pathogenic fungus,molecular identification of antagonistic bacterium and biocontrol mechanism of antagonist.The research results are as follows:The samples of diseased plants from field areas with high incidence of wilt were separated and purified.One fungal strain had been obtained.It was identified as a strain of Fusarium oxysoporum based on its colony morphology and conidial characteristics.The results of pathogenicity test in pot and field demonstrated that it was pathogenic strain of bitter gourd wilt.The soil samples collected from rhizosphere soil of healthy bitter gourd were isolated and purified by grades dilution of soil.7 bacteria strains were obtained.They showed evident antagonistic activity against FOM in plate test.One among 7 strains indicated significant control effect on bitter gourd wilt in pot experiment in greenhouse.Control effect was all above 60%in three tests.After the sequence alignment and analysis of 16S rDNA and gyr B,the dominant strain was identified as Bacillus amyloliquefaciens.Its strain number was named SK2.Primary researches on the control mechanism of bitter gourd wilt by Bacillus amyloliquefaciens SK2 strain were conducted in this experiment.The results showed that after bitter gourd seeds were soaked in bacterial suspension of SK2,The length of radicle was significantly longer than that of the control group,the promoting effect was about 30%.Strain SK2 was a dominant bacteria in rhizosphere.It was able to colonize in the rhizosphere of bitter gourd plant.Activity of defense enzymes in plants of bitter gourd was tested at 2,4,6,8,10,12 days after inoculation of pathogen in both treatment group and control group.The results showed that the activity of polyphenol oxidase(PPO),phenylalanine ammonia-lyase(PAL)and Peroxidase(POD)of bitter gourd plants in the treatment group with SK2 was higher than that in the control group.