Evaluation of Certain Biocides and Chemicals Inducing Resistance in Management of Cucumber Downy Mildew Under Protected Cultivation

Abstract

Downy mildew of cucumber is caused by the fungus-like pathogen Pseudoperonospora cubensis (Berk and Curtis), which causes loss in the yield in Egypt especially under protected cultivation where low temperature and high humidity are prevalent. The efficiency of two Bio-control agents i.e. T34 (Trichoderma asperellum, 10 9 spore/cm 3 ) and Bio-Cure-B (Pseudomonas fluorescens, 10 8 spore/cm 3 ) as well as three resistance inducing chemicals (RICs), i.e. potassium dihydrogenphosphate (K 2 HPO 4 ), salicylic acid (C 7 H 6 O 3 ), and potassium nitrate (KNO 3 ) were evaluated for controlling cucumber downy mildew under greenhouse and plastic house conditions. Greenhouse experiment data revealed that, spraying cucumber plants with either biocontrol agent or tested RICs two times i.e. 5 days before and/or nine days after artificially inoculated by the P. cubensis significantly reduced percentage of disease severity, meanwhile plant length and foliage fresh weight were increased in comparison with control treatments. The treatments increased the activity of peroxidase, β-1,3glucanase, beside increase in total carbohydrates and total phenolic contents. Under plastic house, all tested biocides and/or RICs either alone or double combinations caused significant reduction in disease severity associated with significant increment in some growth parameter of cucumber plants (plant length and fruit yield) when compared with control treatments in both seasons. However, application of tested RICs mixture with tested biocides was more effective in this regard than the only application of them individually. In this respect, tested biocides were also more efficient than resistance inducing chemicals (RICs).