Screening<italic> Streptomyces </italic>against <italic>Xanthomonas axonopodis</italic> pv<italic>. glycines</italic> and study of growth-promoting and biocontrol effect

Abstract

<p id="C3">Soybean bacterial pustule disease occurs globally, seriously affecting soybean production. To avoid the many shortcomings of chemical fungicides, the addition of biocontrol bacteria has gradually become an alternative strategy for the prevention and treatment of soybean bacterial pustule disease. However, there are few reports on the development and prevention of soybean bacterial pustule disease biocontrol agents. In this experiment, a total of 186 strains of actinomycetes were isolated from a variety of plant rhizosphere soil samples using the gradient dilution coating method. Eight strains of actinomycete with antagonistic resistance to <italic>Xanthomonas axonopodis</italic> pv. <italic>glycines </italic>(<italic>Xag</italic>) were screened by coculture and Oxford cup methods. Among them, the strain Sl-3 performed the strongest antibacterial activity and the inhibition zone diameter was (32.5±1.5) mm. According to morphological characteristics, physiological and biochemical experiments, 16S rDNA sequencing and phylogenetic analysis, the strain Sl-3 was identified as <italic>Streptromyces lilacinus</italic>. The crude ethyl acetate extract of <italic>Streptromyces lilacinus</italic> Sl-3 has a good inhibitory effect on the growth of <italic>Xag</italic>. The lowest inhibitory concentration of the crude extract was determined to be 64 μg mL ^-1 by 96-well plate method. Scanning electron microscopy revealed that the crude extract of strain Sl-3 had a certain damage effect on <italic>Xag </italic>cells, which affected cell division and cell membrane synthesis, thus inhibiting the growth of bacteria. The crude extract also inhibited the production of<italic> Xag</italic> exopolysaccharide, affected the formation of biofilm, and reduced the toxicity of <italic>Xag</italic> infection. The results of fourier transform infrared spectroscopy showed that the chemical and physiological indexes of lipids, proteins and nucleic acids on the surface of <italic>Xag</italic> cells were affected by crude extract treatment, leading to changes in the structure and composition of <italic>Xag</italic> cell surface substances. The growth promotion test indicated that the fermentation filtrate of the strain Sl-3 can significantly promote the growth of soybean plants. The pot incubation test revealed that the fermentation filtrate of <italic>Streptomyces lilacinus</italic> Sl-3 had a good control effect on soybean bacterial pustule disease with a relative control effect of 93.17%, and the early prevention effect was better than the treatment after the onset.