Biocontrol of Phytophthora Root and Stem Rot and Growth Promotion of Soybean Plants by the Rhizobacterium Enterobacter pseudoroggenkampii Strain GVv1 Isolated from Vicia villosa Roth

Abstract

Phytophthora root and stem rot (PRSR) caused by Phytophthora sojae is a major concern for global soybean production. To identify a bacterial biocontrol agent against PRSR, 73 rhizobacterial strains were isolated from wild and cultivated legumes and screened for their protective activities against PRSR in pot experiments. Strain GVv1 was selected for its consistent protective effect through repeated pot experiments. The protective effect of this strain was similar to that of the fungicide mancozeb-metalaxyl. A dual-culture assay showed that GVv1 produced antifungal metabolites effective against P. sojae. To evaluate the potential adaptability of GVv1 to the soybean rhizosphere environment, its growth was examined in soybean root exudates and nutrient medium, both supplemented with daidzein, an antimicrobial isoflavone secreted by soybean roots. GVv1 proliferated using soybean root exudates and had sufficient tolerance to daidzein to colonize the soybean rhizosphere. The plant growth-promoting effect of GVv1 on soybean plants was also investigated. GVv1 significantly increased shoot and root dry weights, indicating its plant growth-promoting activity. In vitro assays showed that GVv1 produced indole-3-acetic acid, siderophores, and 1-aminocyclopropane-1-carboxylate deaminase and solubilized insoluble phosphates. A taxonogenomic analysis of the draft genome identified GVv1 as Enterobacter pseudoroggenkampii with high similarity (98.32% average nucleotide identity) to E. pseudoroggenkampii strain 155092T. To the best of our knowledge, this is the first study to report the biocontrol and plant growth-promoting activities of E. pseudoroggenkampii.