Efficacy of Two Bacillus subtilis Strains CHFA and CHFB Against Soybean Cyst Nematode Heterodera glycines

Objective The soybean cyst nematode (SCN), Heterodera glycines, is one of the most economically important plant-parasitic nematodes. This pest poses a severe threat to soybean〔Glycine max (L.) Merr.〕 production. To explore the promising biocontrol bacterial resources for managing SCN, we conducted a series of laboratory and field studies to assess the nematicidal property and biocontrol efficiency of two Bacillus subtilis strains, CHFA and CHFB.

Method In vitro assays were performed to determine the effects of different concentrations (1, 5, 10 times) of fermentation filtrates from CHFA and CHFB on SCN egg hatching and second-stage juvenile (J2) mortality rates. Pot experiments were used to analyze the impact of these filtrates on SCN infection, development and reproduction. Field experiments were conducted to evaluate the suppressive effects of soybean seeds coated with CHFA or CHFB on cyst density in Daqing and Heihe SCN-infested fields, and their impact on soybean growth and yield.

Result Our findings revealed that the fermentation filtrates of CHFA and CHFB exhibit nematicidal activity, with 56.94% and 61.40% corrected J2 mortality rates after incubation with 1×concentration of filtrates for 24 hours, respectively. 1× CHFA and CHFB filtrates also inhibited egg hatching by 75.67% and 82.30%, respectively. Pot experiments showed that the filtrates from two strains significantly reduced SCN infection and decreased the number of cysts and eggs on soybean roots (P < 0.05). Application of CHFA and CHFB caused the highest inhibition rates of 45.52% and 56.55% against nematode infestation, respectively. The reduction rates for cyst number were 40.83% and 49.58%, while the inhibition rates for eggs reproduction were 45.16% and 43.92%. Furthermore, CHFA and CHFB displayed the growth promoting potential on soybean plants. In Heihe field experiment, seed coating with CHFA and CHFB exhibited the control effects on the cyst density of SCN, with reduction rate of 43.87% and 56.78%, respectively. In Daqing test field, the control efficacy of CHFA and CHFB against SCN reached 58.04% and 55.85%. Additionally, CHFA and CHFB treatments also resulted in an improvement in soybean growth under field conditions.

Conclusion These results demonstrated that the two B. subtilis strains, CHFA and CHFB had both soybean growth promoting potential and the control efficiency against SCN in pot and field experiments. Hence, the present study provided valuable information to optimize the use of CHFA and CHFB as biological agents for controlling plant nematodes.