Selection of Bacillus strains as potential candidate against pathogenic Fusarium occurring on cereal.

Fusarium species are among the most important fungal pathogens of cereals able to synthetize harmful mycotoxins. The most important cereal diseases are caused by co-occurrence of multiple Fusarium species, mainly F. graminearum and F. culmorum, producers of deoxynivalenol, and F. proliferatum, producer of fumonisins. Nowadays, the increasing interest to reduce chemicals in agriculture, prompts researchers to select new eco-friendly strategies against fungal diseases. This study aimed to select potential bacterial bio-control agents to control Fusarium species. Forty-eight Bacillus strains belonging to Bacillus velezensis, B. amiloliquefaciens, B. subtilis, B. licheniformis, B. mojavensis, B. simplex, B. megaterium, B. oleronius, B. pumilus and B. safensis, isolated from wheat and maize kernels, were considered. The antagonistic activity against F. graminearum, F. culmorum and F. proliferatum species, by co-colture assay, and the antimicrobial effect of bacteria filtrates were evaluated. Twenty-three strains, including all B. velezensis and B. amyloliquefaciens strains, showed a good antagonistic activity, with mycelial growth inhibition values up to 70%. Moreover, 14 strains produced active compounds inhibiting mycelial growth up to 60%. To elucidate the molecular mechanisms associated to the activity of these strains against Fusarium species, all selected strains were screened for the presence of genes involved in the synthesis of active biomolecules, including surfactin, fengycin, iturin, bacillomycin, bacilysin, difficidin and mycosubtilin. The gene fragments were also sequenced and analysed, to identify, among and within Bacillus species, possible polymorphisms associated to the different capability to inhibit Fusarium growth. In addition, the effect of Bacillus strains on deoxynivalenol and fumonisin production when co-cultured with Fusarium strains, was also studied. Although any effect was observed in fumonisin production, half of Bacillus strains inhibited completely DON production.