Bacillus sp. FSQ1: a Promising Biological Control Agent Against Sclerotinia sclerotiorum, the Causal Agent of white Mold in Common Bean (Phaseolus vulgaris L.)

Abstract

Abstract Phytopathogenic fungi cause several diseases in the common bean (Phaseolus vulgaris), diminishing its productivity, i.e. white mold. This work aimed to isolate and characterize the causal agent of the white mold disease observed in a common bean commercial field, in Northern Mexico; as well as to identify a promising native biological control agent against this phytopathogen. Based on macro/microscopic traits (white-cottony mycelium, and sclerotia formation) and molecular identification [sequencing of the internal transcribed spacer 1 (ITS1) gene], a fungal isolate (FRM18) obtained from symptomatic common bean plants, was identified as Sclerotinia sclerotiorum. In addition, a bacterial strain (FSQ1) isolated from the common bean rhizosphere showed in vitro antagonism against S. sclerotiorum FRM18, inhibiting 2.4 ± 0.2 cm of the studied phytopathogen growth. Based on macro/microscopic traits (gram-positive bacteria, bacillary morphology, and endospore production) and molecular identification (sequencing of the 16S rRNA gene), strain FSQ1 was affiliated to the genus Bacillus. Common bean plants inoculated with S. sclerotiorum FRM18 showed a height reduction of 25% at day: 60 and white mold disease was observed (compared to un-inoculated plants), validating the Koch’s postulates, which confirm that strain FRM18 is the causal agent of this disease in the field. However, common bean plants co-inoculated with S. sclerotiorum FRM18 and Bacillus sp. FSQ1 (compared to un-inoculated plants) were not affected in their development, and symptoms of the disease were not observed. Even when lipopeptides are the potential action mode of Bacillus sp. FSQ1 to inhibit S. sclerotiorum FRM18, further researches are necessary to determine the main antimicrobial compounds produced by strain FSQ1.

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