Biological Control of Powdery and Downy Mildews of Cucumber Under Greenhouse Conditions

Powdery and downy mildews are potentially serious diseases of cucumber inflicting considerable quantitative and qualitative losses. Efficacy of Bacillus subtilis, Pseudomonas fluorescens, Derxia gummosa and Trichoderma harzianum to control both diseases on cucumber plants under greenhouse conditions was studied. Spray of cucumber plants with suspensions of these bioagents significantly reduced severity of both mildews as well as increased fruit yield (Kg/plant) compared to the control. B. subtilis recorded highest reduction of area under disease progress curve (AUDPC), being 175.0 as compared to 536.55 in the control for powdery mildew, while T. harzianum recorded highest reduction being 241.15 as compared to the control (513.45) for downy mildew. Light and scanning electron microscopy showed that Podosphaera fusca and Pseudoperonospora cubensis spores and hyphae were abnormal and both pathogens had restricted growth on treated-cucumber plants. Additionally, treated plants showed significant increase in plant growth parameters (plant height, total chlorophyll and fresh and dry weight) and the activity of defense related enzymes (peroxidase and polyphenoloxidase) compared to the untreated plants. The results suggest the possible use of B. subtilis, T. harzianum and P. fluorescens to control powdery and downy mildews on cucumber.