Isolation, characterization and identification of novel broad spectrum bacterial antagonist(s) to control Fusarium wilt of eggplant

Soil bacteria are now-a-days familiar for plant disease prevention in comparison to chemical control measures in an eco-friendly way. Antagonistic soil bacteria have created tremendous interests among scientists to be an alternative means of plant disease control. The aim of our study was to isolate soil bacteria with a multifaceted role, both in the aspects of plant nutrition and disease prevention. To achieve our goal, rhizobacteria from crop plants, cultivated in different regions of West Bengal were isolated and from a total of 250 isolates, only eight were primarily selected based on their initial growth suppression capabilities against the phytopathogen Fusarium oxysporum. Finally, the two bacterial isolates, NC1 and NC2, showed in vitro broad-spectrum antifungal activity against seven potent phytopathogenic fungi, i.e., Fusarium oxysporum, Alternaria alternata, Colletotrichum capsici, Macrophomina phaseolina, Sclerotium hydrophilum, Rhizoctonia solani and Penicillium digitatum, where they suppressed mycelial growth up to 69% over untreated control. The two potent antagonists were screened in vitro for their plant growth promoting (PGP) and antifungal properties where they showed their efficacy to produce many lytic enzymes, indole acetic acid (IAA) and ammonia. The isolates were detected as Gram-positive, endospore, and capsule forming rod-shaped bacteria. On the basis of morphological, physiological, biochemical and BLAST analysis of 16s rDNA sequences, NC1 and NC2 were identified as Bacillus amyloliquefaciens KY568716 and Bacillus velezensis KY568715. When applied on eggplant, both the isolates suppressed Fusarium wilt symptoms and enhanced plant growth significantly. The effects were observed up to 30 days after pathogen inoculation and both the isolates were effective in reducing Fusarium wilt disease symptoms by 57.23% and 64.19% respectively, as compared to pathogen treated plants. They also showed significant enhancement of all plant growth parameters such as root and shoot length, biomass and chlorophyll content. Thus, the two isolates can be used to develop an effective dual function bio-control agents to control plant diseases as well as promoting plant growth.