Sclerotinia sclerotiorum causes serious yield losses in oilseed crops worldwide. Bacillus subtilis Tu-100 significantly reduced (P <= 0.05) the incidence of disease caused by S. sclerotiorum on oilseed rape at harvest in two trials conducted in fields artificially infested with this pathogen. Mean plant dry weight was significantly greater (P <= 0.05) and mean plant length was significantly greater (P <= 0.07) at the seven-true-leaf stage with the Tu-100 treatment than with the control. Mean seed yield per 120 plants at harvest was significantly greater (P <= 0.05) in the second field trial with treatments containing isolate Tu-100. B. subtilis Tu-100 also promoted the growth of hydroponically grown oilseed rape. Plants were approximately 15% greater in dry weight (P <= 0.0001) and 6% greater in length (P <= 0.0025) when grown in the presence of isolate Tu-100 in Hoagland's solution, compared with the noninoculated control. In gnotobiotic studies, the lacZ-tagged strain B. subtilis Tu-100(pUC18) was detected within all roots of oilseed rape. Isolate Tu-100 did not persist in the ectorhizosphere of oilseed rape. Populations of this isolate decreased from 8.5x10(8) colony-forming units (CFU) per seed to approximately 10(2) CFU in the plant ectorhizosphere within 30 days of sowing in autoclaved soil.