Evaluation of the antagonistic activity of Bacillus amyloliquefaciens against fungal pathogens of wheat

Abstract

Wheat is one of the most important crop all over the world and its widespread diffusion makes it constantly exposed to many abiotic and biotic stresses. Among the latter, pathogenic fungi represent a serious threat to the cultivation of this cereal. Nowadays the use of biocontrol agents (BCAs) is one of the most successful strategies for the prevention and control of plant diseases. This study deals with (i) the in vitro evaluation of the antifungal activity of three strains of B. amyloliquefaciens against Fusarium graminearum, Fusarium culmorum, Bipolaris sorokiniana and Septoria tritici, (ii) the molecular and chemical characterization of the compounds involved in the activity, (iii) the in vivo evaluation of the antifungal activity against B. sorokiniana and (iv) the in vivo wheat growth promotion carried out by B. amyloliquefaciens strains. The inhibitory action showed by the filtrates and the extracts of the bacterial growth broths against all the tested pathogens highlighted the nature of the molecules involved, that are released, liposoluble and thermostable. The analysis of the presence of ituA, fenD, surfA, bmyB and mycA genes confirmed the potential production of cyclic lipopeptides (cLPs), such as iturin, fengycin, surfactin, bacillomycin and mycosubtilin, that are reported as antifungal compounds. The production of cLPs was confirmed with the characterization of the culture filtrates by FPLC and the antagonistic assays performed with the fractions obtained. It was confirmed that fengycins were mainly responsible of the antifungal activity, especially against B. sorokiniana, that was in vivo inhibited by B. amyloliquefaciens cells and their filtrates. Wheat growth promotion was evaluated on seedlings after treatment with B. amyloliquefaciens suspensions. The three bacterial strains promoted germination of wheat seeds, seedling growth and root development, confirming to be potential biofertilizers for this cereal. The results obtained confirm that B. amyloliquefaciens can be considered a valid BCA against the most important pathogens of wheat, and its use can be recommended in the formulation of commercial bio-pesticides.