SUPPRESSION OF PHYTOPHTHORA NICOTIANAE BY APPLICATION OF BACILLUS-SUBTILIS IN CLOSED SOILLESS CULTURE OF TOMATO PLANTS

Possibilities of biological control of the root pathogen Phytophthora nicotianae by Bacillus subtilis (FZBA) applied ro a closed soilless cu lture of tomato plants (cv. Counter) were investigated. In the effects performed of B. subtilis alone and in combination with the fungicide Propamocarb HCI have also been studied. The tomato plants were first b acterized in the 3-leave stage and later, after planting, a second tim e by introduction of B. subtilis in the circulating nutrient solution. During giant growth population density of B. subtilis in the nutrient solution and on the root surface was determined, and at three dates t he population density of heterotrophic microorganisms was also investi gated. Dry weight of shoot and root of tomato plants were significantl y reduced by inoculation of P. nicotianae. Compared to the untreated c ontrol fruit yield was significantly higher after application of B. su btilis. Control of P. nicotianae by the fungicide (Propamocarb HCI) al so resulted in a significant increase of fruit yield compared with the P. nicotianae treated control plants. Furthermore, a higher fruit yie ld was observed if plants infected with P. nicotianae were treated wit h B. subtilis. The successful control of P. nicotianae by a combined a pplication of B. subtilis and Propamocarb HCI appears not to be synerg istic. During the 11 weeks of plant growth a stable colonization by B. subtilis could be observed on the root surface, while in the nutrient solution population density decreased with time but remained constant in the root-mat. The density of heterotrophic microorganisms on the r oot surface and in the nutrient solution was not influenced by bacteri zation of tomato plants and nutrient solution.