Multifaceted Bacillus spp. for the management of cotton bacterial blight caused by Xanthomonas citri pv. malvacearum

Bacterial antagonists against plant pathogens are widely exploited for the biological management of plant dis-eases. In the present study, antagonists were isolated from cotton plant associated bacteria such as endophytes (74 isolates), phylloplane (32 isolates) and cotton rhizosphere soils (48 isolates). Their efficacy against X. citri pv. malvacearum (Xcm) were evaluated in vitro by agar well diffusion technique. Among the isolates, the endophyte Bacillus amyloliquefaciens strain ETL2 was very effective in inhibiting the Xcm growth with an area of 983.76 mm2 followed by Bacillus velezensis strain ELS2 with an area of 944.41 mm2. PCR amplification of antimicrobial peptide (AMP) genes revealed that B. amyloliquefaciens strain ETL2 had maximum of 8 antibiotic biosynthesis genes namely, ItuC , bacA , bacD , bamC , fenCEA , sfrA , spaCS and mycC that produced antibiotics Iturin, bacilysin, bacillomycin, fengycin, surfactin, subtilin and mycosubtilin. Further, B. amyloliquefaciens strain ETL2 associated with Xcm inhibition was identified as aromatic hydrocarbons, phenols and fatty acids by Gas chromatography and mass-spectrometry (GC-MS) analysis of culture extracts. Delivery of B. amyloliquefaciens strain ETL2 and B. velezensis strain ELS2 as seed treatment and foliar spray was found promising for the management of bacterial blight of cotton in pot and field experiments. In pot and field experiments, the maximum plant growth promotion and seed cotton yield were observed in the plants treated with B. amyloliquefaciens strain ETL2 followed by B. velezensis strain ELS2 with better disease control efficiency compared to chemical control agents and chemical plant defense inducers.

Automated summary

Bacterial antagonists were isolated from cotton plant associated bacteria and evaluated for their efficacy against X. citri pv. malvacearum in vitro. Bacillus amyloliquefaciens strain ETL2 was found to be highly effective in inhibiting bacterial growth, followed by Bacillus velezensis strain ELS2. PCR amplification of antimicrobial peptide (AMP) genes revealed that B. amyloliquefaciens strain ETL2 had the highest number of antibiotic biosynthesis genes, and GC-MS analysis confirmed the presence of aromatic hydrocarbons, phenols, and fatty acids in the culture extracts of ETL2. Field experiments showed that seed treatment and foliar spray with ETL2 and ELS2 resulted in optimal plant growth and cotton yield, as well as effective disease control.