Abstract Bacillus subtilis 916 was an effective biocontrol
agent in control rice sheath blight caused by Rhizoctonia
solani. To further improve its antagonistic ability, lowenergy
ion implantation was applied in Bs-916. We studied
the effects of different doses of N+ implantation. The
optimum dose of ion implantation for the Bs-916 was from
15×2.6×1014 N+
/cm2 to 25×2.6×1014 N+
/cm2
. The mutant
strain designated as Bs-H74 was obtained, which showed
higher inhibition activity in the screening plate. Its
inhibition zone against the indicator organism increased
by 30.7% compared to the parental strain. The control
effect of rice sheath blight was improved by 14.6% over
that of Bs-916. Thin-layer chromatography and highperformance
liquid chromatography analysis indicated that
lipopeptides produced by Bs-916 and the mutant strains
belonged to the surfactin family. Bs-H74 produced approximately
3.0-fold surfactin compared to that of Bs-916. To
determine the role of surfactin in biocontrol by Bs-916, we
tested another mutant strain, Bs-M49, which produced
lower levels of surfactin significantly, and found that BsM49
had no obvious effects against R. solani. These results
suggested that the surfactin produced by Bs-916 plays an
important role in the suppression of sheath blight. These
observations also showed that the Bs-H74 mutant strain is a
better biocontrol agent than the parental strain.