Bacillus subtilis TE3: A promising biological control agent against Bipolaris sorokiniana, the causal agent of spot blotch in wheat (Triticum turgidum L. subsp. durum)

Abstract

Bipolaris sorokiniana, the causal agent of wheat spot blotch, is an emerging phytopathogen in the Yaqui Valley, Sonora, Mexico. Currently, the unique method to control spot blotch on that region is employing synthetic fungicides with environmental and human health issues. Thus, the aim of this work was to identify and characterize native wheat-associated bacteria in order to find promising biological control strains that can be used as a sustainable alternative to control spot blotch. The identification of antagonistic strains was carried out by confrontation assay against B. sorokiniana. Antagonistic strains to B. sorokiniana were taxonomically classified by 16S rRNA gene sequencing, and characterized on important biological traits: (i) inhibition of the target phytopathogen, (ii) growth rate, and (iii) cytotoxic activity. Out 195 bacterial strains tested, 14 exhibited antagonistic activity against B. sorokiniana at different degree (1.6–8.0 mm of inhibition zone). The Antagonistic strains were taxonomically identified as members of Bacillus (eight strains), Paenibacillus (one strain), Pseudomonas (two strains), Achromobacter (one strain), Delftia (one strain), and Stenotrophomonas (one strain). The strain TE3, identified as Bacillus subtilis, showed promising biological control traits: (i) broad spectrum inhibition against B. sorokiniana, (ii) growth capacity in synthetic minimal medium, and (iii) non-cytotoxic activity to erythrocyte (γ-hemolysis). The application of cell suspension or cell-free culture filtrate of B. subtilis TE3 under highly conducive conditions (28 °C and 100% HR) for wheat spot blotch, resulted in a significant reduction of that disease. In conclusion, B. subtilis TE3 and its antifungal metabolites are promising effective treatment to control the causal agent of the wheat spot blotch.