Abstract
The effect of potassium phosphite (KPhi) on the photosynthetic parameters of cucumber plants inoculated with Pseudoperonospora cubensis was investigated in the present study. Cucumber plants were treated with KPhi before or after inoculation with P. cubensis and leaf samples were collected at different time courses for assessments. Results showed that in pathogen-inoculated plants Fv/Fm was decreased up to 3%. The rate of quantum photosynthetic was also decreased significantly in inoculated plants. Downy mildew led to a decrease in chlorophyll amount which in turn reduced the efficiency of photosystem II. In the KPhi-treated leaves, chlorophyll a and b decreased by 72% and 68%, respectively. Remarkable reduction in the efficiency of photosystem II as well as increased lipid membrane disruption, led to increased lipid peroxidation rate of the membranes up to 52%. The results of this study indicate the mitigating role of potassium phosphite in reducing the adverse effects of pathogen and maintaining the photosynthetic apparatus efficiency in cucumber plants.
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