Bacillus subtilis strain NCD-2 is strongly antagonistic toward phytopathogenic fungi, and functions as an
excellent biocontrol agent for cotton soil-borne diseases. The aims of this study were to characterize the
main active antifungal compound from strain NCD-2 and clarify its role in suppressing cotton dampingoff
disease. Strain NCD-2 and lipopeptide extract prepared from an NCD-2 culture strongly inhibited
the growth of Rhizoctonia solani in vitro. The lipopeptides of strain NCD-2 were separated by fast protein
liquid chromatography (FPLC) and the antifungal compound was identified as a cluster of fengycin
homologs analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. A
fengycin-deficient mutant was obtained by in-frame deletion ofthe fengycin synthetase gene in B. subtilis
NCD-2. Compared with the wild-type strain,this mutant showed decreased abilities to inhibitthe growth
of R. solani in vitro and to suppress cotton damping-off disease in vivo. Studies showed that the population
of fengycin-deficient mutant was almost same as that of the wild-type NCD-2 strain in the cotton
rhizosphere. However, the population of R. solani in the cotton rhizosphere colonized by the fengycindeficient
mutant was twice that in the cotton rhizosphere colonized by the NCD-2 wild-type strain. This
study demonstrated thatfengycin-type lipopeptides are the main antifungal active compounds produced
by B. subtilis NCD-2. These compounds play a major role in restricting the population of R. solani in the
cotton rhizosphere and in suppressing cotton damping-off disease.