Isolation and characterization of antagonistic bacteria against fusarium wilt and induction of defense related enzymes in banana

Abstract

Fusarium wilt caused by Fusarium oxysporum is considered a fatal disease to bananas.Chemical control of Fusarium wilt in bananas has received little efficiency. Alternatively, biological control is a viable strategy against soil-borne diseases. The objectives of this research were to isolate antagonistic bacteria and investigate the possible mechanisms against Fusarium wilt. An antagonistic Bacillus strain, termed KY-21 against F. oxysporumf. sp. Cubense was isolated from the soil of banana’s rhizosphere by dual culture. The strain was identified as Bacillus subtilis according to the characteristics of its morphology and by homology analysis of its 16S rDNA sequence. Mycelium growth of the pathogen was seriously inhibited after treatment with the fermentation filtrate of KY-21. Observation revealed that the tips of the hypha were deformed into spherical structures that were remarkably constricted. The strain KY-21 displayed a good ability to colonize and can transfer into banana tissues. The activities of polyphenol oxidase (PPO) and peroxidase (POD) in bananas showed an increase after inoculated with KY-21, compared to control.In vivo biocontrol assays showed a significant reduction in wilt index and vascular discoloration. These results indicated that the antagonistic mechanisms against Fusariumwilt were involved in the inhibition of mycelial growth and the improvement in activity of defense related enzymes.   Key words: Fusarium oxysporum f. sp. Cubense, antagonistic bacteria, screen,colonization, enzyme activity.