Screening and identification of antagonistic Bacillus vallismortis B against cucumber Fusarium wilt and its biological effect

A bacterial strain B,antagonistic against cucumber Fusarium wilt pathogen(Fusarium oxysporum f.sp.cucumerinum)was isolated from the rhizosphere soil of cucumber.Based on the morphological,physiological and the 16S rRNA gene sequence analysis,the strain B was preliminarily identified as Bacillus sp..Strain B also had antagonistic effects against several pathogenic fungus,such as Verticillium dahliae Kleb,Fusarium oxysporum f.sp.melonis and Phytophthora capsici.fenB,bam,ituA,ituB,ituC and ituD,responsible for the synthesis of antibiotics Fengycin,Bacillomycin and Iturin respectively were identified in strain B.Strain B was inoculated in organic fertilizer(OF)for preparing bio-organic fertilizer(BIO).The effects of OF and BIO in controling cucumber Fusarium wilt were studied in pot experiments.The results showed that the applications of BIO could decrease the incidence of cucumber Fusarium wilt by 66.7% and disease index by 67%,and the biocontrol efficiency was about 80.7%.On the contrary,the application of OF increased the wilt incidence.The application of BIO could significantly promote the growth of cucumber and increase the population of bacteria and actimomyces in rhizosphere soil and decrease the population of fungi and Fusarium oxysporum.The application of BIO also could promote the SOD,POD and CAT activity in cucumber.It is concluded that the application of bio-organic fertilizers is an effective way to control the cucumber Fusarium wilt.