Efficacy of Bacillus subtilis strain QST 713 (Rhapsody) against four major diseases of greenhouse cucumbers

摘要

Diseases of cucumber (Cucumis sativus L.) are a major limiting factor during commercial greenhouse production of the crop. The biological control agent Bacillus subtilis strain QST 713 (Rhapsody, containing 1 x 10(9) colony-forming units per g) was evaluated for efficacy against four major diseases affecting greenhouse cucumbers grown in British Columbia, Canada. These diseases included powdery mildew, Fusarium root and stem rot, Pythium crown and root rot, and gummy stem blight. Rhapsody was applied as a root drench or spray to leaves or flowers at a rate of 1.0 L product/100 L water, or in some experiments at 1.5 L product/100 L water. Applications were made 1 and 4 days prior to, as well as after, pathogen inoculation. Weekly foliar applications of Rhapsody significantly (P = 0.05) reduced powdery mildew colony development and showed eradicative effects on established leaf infections. Leaf area infected on untreated plants was 80-100% compared to 15-20% on Rhapsody-treated plants. Two drenches of Rhapsody made 1 and 4 days prior to Fusarium inoculation significantly (P = 0.05) improved plant growth (height and dry weight) after five weeks, but growth was lower compared to the noninoculated control plants. Treatments made 1 and 4 days post-inoculation were much less effective in preventing disease development. Application of Rhapsody to Pythium-inoculated plants, prior to or after inoculation, did not significantly increase plant height or dry weight compared to the pathogen-only treatment. Developing cucumber fruit inoculated with a mycelial suspension of the gummy stem blight pathogen caused 24-30% post-harvest decay after fruit were incubated at 20-22 degrees C for 7-10 days. Fruit infection was reduced by almost 55% when Rhapsody was applied 24 h prior to pathogen inoculation while an application made 24 h after pathogen inoculation had no effect. Preventative applications of Rhapsody were effective in reducing development of powdery mildew, Fusarium root and stem rot, and gummy stem blight on cucumber, while eradicative applications were effective against powdery mildew only. There was no effect observed against Pythium root rot.