Characterization and evaluation of Bacillus altitudinis BS-4 as a novel potential biocontrol agent against Phytophthora sojae in soybean

Soybean Phytophthora root rot (PRR) caused by Phytophthora sojae is one of the most devastating diseases of soybean worldwide. This study was conducted to develop new effective biocontrol agents for the control of the disease and explore the action mechanism. Eleven antagonistic bacterial strains against P. sojae were isolated from the soybean field soil samples, and among the strains, BS-4 not only had the strongest inhibitory activity against P. sojae, but also had good inhibition to other four species of oomycetes in Phytophthora and eight fungal pathogens. Based on 16S rDNA sequence analysis and the physiological and biochemical properties, the strain BS-4 was identified as Bacillus altitudinis. Strain BS-4 culture filtrate had significant inhibitory effects on the pathogens, and the inhibition rates were stronger than those in the dual culture. BS-4 filtrate kept a high bioactivity to P. sojae at a high temperature, even at 121℃, and in the pH range of 5 to 12. The germination of zoospores and the formation of sexual organs were seriously affected by BS-4 filtrate. Furthermore, detached leaf assays and greenhouse experiments showed that BS-4 suspension and culture filtrate all had good disease control efficacy, and in the field experiment, BS-4 suspension reduced the disease index and increased the biomass of soybean shoots and roots, significantly (P < 0.05), with control effect of 75.29% on PRR. It is suggested that B. altitudinis strain BS-4 is a novel potential biocontrol agent to control PRR, and will have a broad application prospect in PRR biocontrol.