EFFECTS OF STREPTOMYCES CORCHORUSII, STREPTOMYCES-MUTABILIS, PENDIMETHALIN, AND METRIBUZIN ON THE CONTROL OF BACTERIAL AND FUSARIUM-WILT OFTOMATO

Two Streptomyces spp. and two herbicides were used to control the path ogens of tomato wilt disease in vitro and in vivo. In vitro studies sh owed inhibitory effects of Streptomyces corchorusii against Fusarium o xysporum f.sp. lycopersici (Sacc.) and inhibitory effects of Streptomy ces mutabilis against Pseudomonas solanacearum. In cultures amended wi th pendimethalin or metribuzin, the growths of P. solanacearum and F. oxysporum were inhibited. The degree of growth inhibition was proporti onal to the herbicide concentration, with pendimethalin being more eff ective than metribuzin, and maximum inhibition was at 2.0 x 10(-3) M. The growth of S. corchorusii and S. mutabilis was slightly inhibited o r enhanced by the herbicides. Supplementation of the herbicides to cul ture media of the antagonistic Streptomyces spp. increased their inhib itory effects against P. solanacearum and F. oxysporum that were propo rtional to the herbicide concentrations. Soaking seeds of tomato in th e herbicides prior to sowing in sterilized and raw soils and applying S. corchorusii and (or) S. mutabilis to the soils artificially infeste d with P. solanacearum and (or) F. oxysporum f.sp. lycopersici (Sacc.) 40 days after transplanting revealed significant interactions that ga ve better control of wilt than either applied alone. The combination o f antagonistic Streptomyces spp. was more effective with pendimethalin than with metribuzin and in nonsterilized soil than in sterilized soi l. The combination of pendimethalin with S. corchorusii, S. mutabilis, or S. corchorusii plus S. mutabilis was more effective than the singl e treatment with microbial antagonists or the herbicide against F. oxy sporum, P. solanacearum, and Pseudomonas plus Fusarium, respectively. In both soils, the combination of microbial antagonists with pendimeth alin was most effective at 2.0 x 10(-3) M, disease incidence being red uced to zero and the percent colonization of either pathogen being the lowest. The results also revealed that these combinations minimized t he negative effects of the pathogens on tomato growth. This work demon strates that two compatible control agents, biological and chemical, c an be combined to give additional control of a plant pathogen.