Identification Of An Antagonistic Bacillus Strain And Characterization Of Its Efficacy And Mechanisms In Suppression Of Sclerotinia Disease On Lettuce

This study obtained a Bacillus strain Bs9-1 which was strongly antagonistic against Sclerotinia sclerotiorum,the causal agent of lettuce stem rot.It was identified as B. subtilis on the basis of characterization of morphological,physiological/biochemical features,and its 16S rDNA sequence(GenBank accession NO.EU753871).Both liquid cultures and cell-free cultural filtrates of Bs9-1 could inhibit the mycelial growth of S.sclerotiorum with the efficacy of 81.3%and 78.3%,respectively.Cytoplasm of the inhibited hyphae of S.sclerotiorum became granularized and exuded.The antifungal substances produced by Bs9-1(AFS_Bs9-1) could delay germination of sclerotia of S.sclerotiorum and inhibit the germination of ascospores of this pathogen.Except for S. sclerotiorum,antagonism of Bs9-1 against other pathogenic fungi including Exserohilum turcicum,Bipolaris maydis,Pyricularia grisea,Botrytis cinerea and Rhizoctonia solani was observed.The antifungal substances produced by Bs9-1 was thermal stable at 40-100℃,but was unstable at 121℃.The activity of the AFS_Bs9-1 was relatively high under the acidic conditions,but was relatively low under the alkaline conditions.Two genes responsible for synthesis of AFS,including sfp for synthesis of surfactant and ituA for synthesis of iturin,were amplified from the genomic DNA of Bs9-1,whereas fenB for synthesis of fengycins was not detected.Under greenhouse conditions,cultures of Bs9-1 and the cell-free cultural filtrates of this bacterial strain were effective in suppression of the infection of lettuce leaves by S. sclerotiorum with the efficacy of 78.2%and 81.2%,respectively.On the other hand, suspensions of the bacterial cells of Bs9-1 were not effective with the efficacy of 8.2%.These results laid a solid foundation for exploitation of Bs9-1 as a biocontrol agent against Sclerotinia diseases of lettuce in the future.