CONSTRUCTION OF RAPD-GENERATED DNA PROBES FOR THE QUANTIFICATION OF BACILLUS-SUBTILIS-FZB-C AND THE EVALUATION OF ITS BIOCONTROL EFFICIENCYIN THE SYSTEM CUCUMIS-SATIVUS-PYTHIUM-ULTIMUM

The aim of biological control in horticulture and agriculture is the p rotection of plants from pathogens using the pathogen's naturally occu rring antagonists. it is assumed that biological methods have less und esirable side-effects on ecosystems than pesticides. Since the risk of horizontal gene transfer from genetically manipulated organisms is no t fully known and the administrative registration procedures are lengt hy, it is preferable to use naturally occurring soil isolates as antag onistic bacteria for the suppression of soil-borne plant diseases. Str ain FZB C is a member of a natural Bacillus subtilis group with antago nistic activity against fungal plant pathogens. The efficiency of Baci llus subtilis was tested in the system Cucumis sativus-Pythium ultimum by means of seed inoculation. Between the third and the tenth day aft er sowing, 5 x 10(3) cfu B. subtilis FZB C per cm root were identified and counted due to their typical colony morphology. P. ultimum, which was mixed into the soil, had no negative effect on the Bacillus popul ation. In greenhouse experiments, B. subtilis had an antagonistic effe ct against Pythium ultimum: the emergence rate was increased by 15-30 % with B. subtilis FZB C and by 13-15 % with B. subtilis JH 642. To ov ercome problems related to detection and quantification of B. subtilis FZB C within the autochthonous bacterial community, two specific DNA probes were developed. They can be used by DNA hybridizations and allo w a simple estimation of the specific cell count on the root surface. RAPD probe 1247-250 has no homology to known sequences.