Evaluation of the anti-oomycete bioactivity of rhizosphere soil-borne isolates and the biocontrol of soybean root rot caused by Phytophthora sojae

Abstract

Phytophthora sojae is an important pathogen that causes soybean root rot. In this study, 200 rhizosphere bacteria were isolated from soybean rhizosphere soil. Six rhizosphere strains that showed antagonistic activity against Phytophthora sojae, SN337-SN342, were screened with further confrontation experiments. The biocontrol activities of the 6 strains, especially SN337, were subsequently characterized and evaluated. In vitro experiments showed that SN337, as a newly developed biocontrol agent, had good antagonistic activity against Phytophthora sojae. In the evaluation of soybean growth promotion, a fermented broth of strain SN337 increased shoot height and root length by 13% and 37.5%, respectively, compared with a control. Importantly, the incidence caused by P. sojae decreased in soybean plants treated with SN337. The fermentation broth of strain SN337 also clearly disintegrated zoospores of P. sojae. The biocontrol effects were further investigated based on the changes in rhizosphere soil microorganisms before and after inoculation with pathogens. Compared to P. sojae infection without SN337 treatment, the abundance of bacteria, fungi, actinomycetes and total microbes were increased, whereas P. sojae was decreased in the rhizosphere of soybean infected by P. sojae inoculation with SN337 treatment. The results indicated that strain SN337 played a role in the maintenance of the soybean rhizosphere environment by increasing the proportion of beneficial microorganism in the soil. In this study, the biocontrol effects of strain SN337 were evaluated based on antagonistic activity and biocontrol assays and on soil microbial analysis. Our results provide new practical clues for developing fungicides for the sustainable management of soybean root rot caused by P. sojae.