Antagonistic potential of lipopeptide producing Bacillus amyloliquefaciens against major vegetable pathogens

The study aimed to identify novel antagonistic microorganisms suitable for biological control of diseases in vegetables grown under tropical conditions. Forty seven Bacillus strains were isolated from rhizosphere soils of Trinidad and they were identified as B. amyloliquefaciens, B. subtilis, B. pumilus, B. cereus, B. megaterium, B. mycoides, B. aryabhattai based on 16S rRNA gene analysis. All Bacillus strains were screened for antibiotic lipopeptide genes viz., Iturin A synthetase C (ituC), Iturin A synthetase D (ituD), Bacillomycin D synthetase (BmyB), Bacilysin synthetase A (bacA), Fengycin synthetase (fenD), Surfactin (SrfC) and Zwittermycin A (ZmA). The study revealed the presence of iturin, bacillomycin, bacilysin, fengycin, surfactin and zwittermycin synthesizing genes in B. amyloliquefaciens, B. cereus, B. megaterium and B. pumilus strains. Testing of different Bacillus species against vegetable pathogens revealed greater antagonistic activity of lipopeptide producing B. amyloliquefaciens strains as compared with non-producers. Phylogenetic analysis of Bacillus species based on 16S rRNA gene clearly distinguished the lipopeptide producers from non-lipopeptide producers. The lipopeptide activity and biocontrol potential of B. amyloliquefaciens strains were further demonstrated in lettuce plants against Cercospora leaf spot under a protected cultivation system as a model. The study provided evidence for the biocontrol potential of lipopeptide producing B. amyloliqufaciens strains in the control of disease causing agents in vegetables. These results are promising for the development of bioagents suitable for disease management in tropical conditions.