Identification of antagonistic bacteria against Alternaria tenuissima, and its effect on antagonism

Abstract:

[Objective] This study aimed to screen and characterize antagonistic bacteria against Alternaria tenuissima, the causal agent of jujube shrinking fruit disease, and to study their antagonistic effects. [Methods] Serial dilutions and a dual culture technique were used for screening bacteria. The bacteria were identified based on morphological, physiological and biochemical features, and a phylogenetic analysis was conducted on an alignment of 16S rRNA gene sequences. Evaluation of the control activity and efficacy of fermentation filtrates against A. tenuissima was carried out by a dual culture assay, microscopic inspection and a spore germination test. Crude active proteins were separated by an ammonium sulfate method. [Results] Two strains of bacteria, STO-12 and STO-45, that were isolated and screened from the soil exhibited excellent inhibition against the fungal pathogen. Based on molecular, morphological, physiological and biochemical features, the two strains were identified as Bacillus subtilis. However, the two strains differed in the production of a pigment that was shorter in length in STO-12 than in STO-45. The fermentation filtrate, the supernatant and the cell-free filtrate of both strains exhibited excellent inhibition against the strain MY5 with a dual culture assay. Further effects of the cell-free filtrate of STO-45 on the pathogen included inhibition of germ tube and hyphal growth, and abnormally swollen or degraded hyphae and germ tubes. Crude active extracellular proteins of STO-45 isolated by an ammonium sulfate method proved to restrain the growth of hyphae. [Conclusion] Both STO-12 and STO-45 strains of B. subtilis have potential for the biological control of jujube shrinking fruit disease.