Antagonistic activity of autochthonous strains of Bacillus amyloliquefaciens and Bacillus velezensis against fungi and oomycetes associated to damping off

Abstract

Damping-off disease, caused by a range of phytopathogenic fungi and oomycetes, poses a significant concern to global crop production. The use of antagonistic Bacillus strains represents a promising biocontrol strategy to mitigate these pathogens. This study evaluated the antifungal and anti-oomycete activities of B. velezensis A6, B. velezensis MEP218, B. amyloliquefaciens ARP23, and B. sp. A7 against major phytopathogens associated to Damping-off. Furthermore, we demonstrated that cyclic lipopeptides produced by Bacillus strains are the compounds possessing the antagonistic activity. The HPLC profiles of the cyclic lipopeptides were different even among the same or related species. After purifying each family of cyclic lipopeptides, we determine whether iturins, fengycins, or surfactins were responsible for the antifungal or anti-oomycete activity. Among these compounds, iturin A showed the strongest antifungal/anti-oomycete effect, followed by fengycins. The effectivity in inhibiting the growth of the phytopathogens varied among the Bacillus strains being A6 the most effective one. Alteration in hyphae morphology were evidenced by light microscopy in M. phaseolina and R. solani exposed to cyclic lipopeptides from B. velezensis A6. Soybean seeds coated with the strain A6 or its cyclic lipopeptides and challenged to Macrophomina phaseolina or Rhizotocnia solani showed better germination energy than those treated with the synthetic fungicide, highlighting the potential of B. velezensis A6 as a biocontrol agent for seed protection in sustainable agriculture. These findings underscore the importance of cyclic lipopeptides in biological control and reinforce the efficacy of Bacillus strains as environmentally friendly alternatives to chemical fungicides.