Abstract
Cucumber powdery mildew disease caused by Podosphaera 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, and Serratia marcescens, as well as the fungicide score (Difenoconazole), on cucumber infected with P. xanthii, in vitro and under greenhouse conditions. Results indicated that culture filtrate of the tested bio-agents and the fungicide (control) significantly reduced P. xanthii conidial 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 by B. subtilis significantly 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.
Highlights
Cucumber (Cucumis sativus L.) is one of the most widely grown greenhouse crops
The highest reduction was attributed to the fungicide being (97.19%), followed by B. subtilis (91.17.0%), P. polymyxa (88.47%), and S. marcescens (85.46%) whereas, T. viride and T. harzianum recorded (82.13% and 76.06%) reduction, respectively
Shehata 2014; Rais et al 2017; Prasannath 2017; Tanaka et al 2017). Such results are in harmony with those previously obtained by García-Gutiérrez et al (2013), ElSharkaway et al (2014), Tanaka et al (2017), Hafez et al (2018), and Elsisi (2019) who showed the ability of the bio-agents to inhibit powdery mildew conidial spores germination
Summary
Cucumber (Cucumis sativus L.) is one of the most widely grown greenhouse crops. Powdery mildew is caused by Podosphaera xanthii (Castagne) U. Braun & Shishkoff (formerly Sphaerotheca fuliginea (Schlechend.: Fr) Pollacci) It is a major foliar disease worldwide, reducing crop quality and yield (Rur et al 2018). Due to the harmful effects on the environment because of the use of fungicide (Ozkara et al 2016), Applications of plant growth-promoting rhizobacteria (PGPR) as biotic inducers have a potential in controlling plant diseases (O’Brien 2017) This positive performance of PGPR has a direct and indirect effects on plants, direct promotion by production of metabolites that improves the plant growth, and indirect growth effects by removal of the pathogens via the secondary metabolites production (Sarhan and Shehata 2014; Prasannath 2017)
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