Effective biocontrol of soybean root rot by a novel bacterial strain Bacillus siamensis HT1

One novel bacterial strain isolated from the inter-rhizosphere soil of soybean with effective biocontrol on soybean root rot was identified as Bacillus siamensis HT1 based on phylogenetic, physiological, biochemical, and morphological analyses. At pH 7 and 25 °C, strain HT1 inhibited the growth of two root rot pathogens (i.e., Fusarium oxysporum and Phytophthora sojae) by 82.96% and 82.44%, respectively. Compared with the control groups, the mycelial weights and spore germination rates of these two pathogens were inhibited by 84.77% and 86.70% as well as 81.25% and 83.77%, respectively, showing expansion, deformation, vesicles, and fracture in mycelial morphology. Strain HT1 was effective against seven pathogenic microorganisms with the inhibition rates nearly 60% or higher. In 96 h, the contents of antioxidant protective enzymes in these two pathogens treated with strain HT1 were significantly lower than those of the control groups. Compared with the control group, the enzymatic activities of peroxidase, superoxide dismutase, and catalase were decreased by 296.42 u/gFW/min, 263.00 u/gFW, and 30.01 u/gFW/min, respectively, in F. oxysporum, and were decreased by 288.59 u/gFW/min, 212.39 u/gFW, and 34.59 u/gFW/min, respectively, in P. sojae. This study showed that strain HT1 was a novel, effective biocontrol agent against soybean root rot.