The plant-associated Bacillus amyloliquefaciens strains MEP2 18 and ARP2 3 capable of producing the cyclic lipopeptides iturin or surfactin and fengycin are effective in biocontrol of sclerotinia stem rot disease

Aims: This work was conducted to identify the antifungal compounds produced by two previously isolated Bacillus sp. strains: ARP₂3 and MEP₂18. Both strains were subjected to further analysis to determine their taxonomic position and to identify the compounds responsible for their antifungal activity as well as to evaluate the efficiency of these strains to control sclerotinia stem rot in soybean. Methods and Results: The antifungal compounds were isolated by acid precipitation of cell‐free supernatants, purified by RP‐HPLC and then tested for antagonistic activity against Sclerotinia sclerotiorum. Mass spectra from RP‐HPLC eluted fractions showed the presence of surfactin C₁₅, fengycins A (C₁₆–C₁₇) and B (C₁₆) isoforms in supernatants from strain ARP₂3 cultures, whereas the major lipopeptide produced by strain MEP₂18 was iturin A C₁₅. Alterations in mycelial morphology and sclerotial germination were observed in the presence of lipopeptides‐containing supernatants from Bacillus strains cultures. Foliar application of Bacillus amyloliquefaciens strains on soybean plants prior to S. sclerotiorum infection resulted in significant protection against sclerotinia stem rot compared with noninoculated plants or plants inoculated with a nonlipopeptide‐producing B. subtilis strain. Conclusions: Both strains, renamed as B. amyloliquefaciens ARP₂3 and MEP₂18, were able to produce antifungal compounds belonging to the cyclic lipopeptide family. Our data suggest that the foliar application of lipopeptide‐producing B. amyloliquefaciens strains could be a promising strategy for the management of sclerotinia stem rot in soybean. Significance and Impact of the Study: Sclerotinia stem rot was ranked as one of the most severe soybean disease in Argentina and worldwide. The results of this study showed the potential of B. amyloliquefaciens strains ARP₂3 and MEP₂18 to control plant diseases caused by S. sclerotiorum.