Effective biocontrol of banana fusarium wilt tropical race 4 by a bacillus rhizobacteria strain with antagonistic secondary metabolites

Abstract

Fusarium oxysporum f.sp. cubense Tropical Race 4 (FOC TR4), is one of the newly emerged dreaded pathogens of banana with an established global presence. Fungicides have not been effective in controlling the disease. There are very few effective antagonistic microbes reported for the biological management of this pathogen.In the present study, suppressive soil was selected for isolation of potential biocontrol plant growth-promoting bacteria. The bacterial strain CSR-D4 Bacillus licheniformis was identified with significant antagonistic attributes and plant growth-promoting properties. This strain exhibited a high inhibition percentage (77.59%) against the FOC TR4 pathogen in the dual plate assay. Further, the bioactive metabolite of the strain conferring biocontrol of FOC-TR4 was also identified through the Liquid Chromatography-Mass Spectrophotometry technique. Our analysis revealed the presence of many antifungal metabolites in the isolate CSR-D4, the majority of which were identified as iturin, fengycin, surfactin, and bacillomycin. These results indicated the involvement of metabolites in the antifungal activity of the strain CSR-D4 against FOC TR4. During sick-pots studies taken with susceptible Cavendish banana cultivar Grand Naine, application of B. licheniformis CSR-D4 showed a significant reduction in the disease incidence percentage (10%). B. licheniformis CSR-D4 treated plants also showed enhanced activity of defense-related enzymes such as β-1,3 glucanase, peroxidase, chitinase, polyphenol oxidase, and phenyl-alanine ammonium lyase compared to FOC TR4 alone treated plants that suggest the occurrence of induced host tolerance in Bacillus licheniformis CSR-D4 treated plants. Our results suggest the antagonistic potential of rhizobacterium Bacillus licheniformis CSR-D4 strain through secreted metabolites mediated the effective biocontrol of Fusarium oxysporum f.sp. cubense Tropical Race 4.