Biological Control of Crown and Root Rot and Bacterial Wilt of Tomato by Bacillus subtilis NB22.

Abstract

Antagonistic activities of Bacillus subtilis NB22 (NB22) isolated from a compost against plant pathogenic fungi and bacteria were examined in vitro. NB22 strongly suppressed not only the growth of 19 plant pathogenic fungi tested but also of 8 plant pathogenic bacteria. Its application to the biological control of crown and root rot and bacterial wilt of tomato caused by Fusarium oxysporum f.sp. radicis-lycopersici (FoR) and Pseudomonas solanacearum (Ps), respectively, was carried out in the field. When rice straw was immersed in cultural suspension of NB22 and then mixed into soils infested with FoR, the occurrence of crown and root rot of tomato was significantly reduced. In addition, when combined with steam sterilization, the suppressive effect was conspicuously enhanced and three to four times greater amount of yield was obtained compared with unsterilized control. Occurrence of bacterial wilt of tomato was also suppressed remarkably when the cultural suspension of NB22 was poured into heavily infested soils, and the percentage of dead plant with NB22 was one-third of the control. These results suggest that NB22 has a wide range of antifungal and antibacterial activities and can be used as a prominent agent to control these soilborne diseases of tomato.