Inducing resistance against powdery mildew caused by Sphaerotheca fuliginea in cucumber (cv. Delta Star) was investigated under greenhouse and commercial protected house conditions as fungicides alternatives. Abiotic inducer (K2HPO4), as well as, biotic inducers (propolis extract and filtrate of Bacillus subtilis and Trichoderma harzianum) was sprayed onto the upper two true cucumber leaves. Topas-100 fungicide at recommended dose and water was used as positive and negative control. Further, specific activities of defense-related enzymes (peroxidase, polyphenol-oxidase and chitinase) and phenolic content were spectrophotometrically measured in cucumber leaves before and after inoculation with fungal spores. Results showed that, all abiotic and biotic tested inducers reduced the disease severity on the treated leaves, increased fruit productivity (fruits number/plant and fruits weight/plant) and increased the activities of defense-related enzymes, but in varying degrees as compared with the control. The combination of propolis extract + Bacillus filtrate + Trichoderma filtrate was the superior treatment among all other treatments. Generally, all abiotic and biotic treatments were better than fungicide treatment with some exceptions.
Keywords: Cucumber; powdery mildew; Sphaerotheca fuliginea; induced resistance; phosphate salts; propolis; bioagent filtrates, enzyme activities
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