EFFECTS OF PAENIBACILLUS STRAINS AND CHITOSAN ON PLANT GROWTH PROMOTION AND CONTROL OF RALSTONIA WILT IN TOMATO

The effects of chitosan and sixteen Paenibacillus strains against the wilt pathogen Ralstonia solanacearum were evaluated in vitro and under greenhouse conditions. Chitosan and two Paenibacillus strains, in particular Paenibacillus polymyxa MB02-1007, were found to have strong in vitro antibacterial activities against R. solanacearum. In addition, chitosan applied as soil drench or seed treatment significantly reduced wilt incidence by 72% and 48%, respectively while P polymyxa MB02-1007 as a soil drench or a seed treatment significantly reduced wilt incidence by 82% and 88%. In general, regardless of the application method, plant growth parameters as well as the activities of chitinase and beta-1,3-glucanase in tomato plants were significantly increased by chitosan and P polymyxa MB02-1007 as compared to the corresponding control, both in the absence and presence of R. solanacearum. The growth of tomatoes, however, was promoted by chitosan more as a soil drench than as a seed treatment, while P polymyxa MB02-1007 as a seed treatment was more effective than as a soil drench. This is the first report on the use of chitosan for the control of tomato wilt and promotion of tomato plants. In conclusion, both chitosan and P polymyxa MB02-1007 show promise for plant growth promotion and control of R. solanacearum in tomato. Combining chitosan and P polymyxa may improve disease control, which should be examined in future studies.