Abstract
Cucumber powdery mildew disease caused byPodosphaera xanthii(Castagne) U. Braun & Shishkoff severe disease-causing yield losses worldwide. This research study was conducted to evaluate the efficacy of the tested bio-agents,Trichoderma harzianum,T. viride,Bacillus subtilis,Paenibacillus polymyxa, andSerratia marcescens, as well as the fungicide score (Difenoconazole), on cucumber infected withP. xanthii,in vitroand under greenhouse conditions. Results indicated that culture filtrate of the tested bio-agents and the fungicide (control) significantly reducedP. xanthiiconidial germination in vitro; the reduction percentage ranged between 91.17 and 76.06%. Also, score recorded the highest reduction percentage (97.19%). All treatments significantly decreased the disease severity and area under disease progress curve (AUDPC) post spraying the bio-agents on cucumber plants under greenhouse conditions. Score followed byB. subtilissignificantly decreased disease severity percentage (67.33 and 65.38%, respectively) and AUDPC (322.84 and 342.06) than the untreated control (988.13 AUDPC). Additionally, treated cucumber plants showed a significant increase in plant growth parameters (plant height, total chlorophyll, fresh, and dry weight) and yield parameters (fruit number/plant and fruit weight/plant) as well the activity of defense-related enzymes, i.e., peroxidase (PO) and polyphenol oxidase (PPO), and total phenols content (TPC) compared to the untreated plants.