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W.C. Lin and D.L. Ehret

Long English cucumber (Cucumis sativus L.) plants were treated with one of three nutrient concentrations in combination with two fruit thinning treatments forming a 3 × 2 factorial greenhouse experiment. High nutrient concentration enhanced fruit color at harvest and prolonged shelf life but reduced marketable fruit per plant. Thinning of one-third of the fruit from the main stem and laterals had a similar effect. Cucumbers harvested from the upper canopy generally had longer shelf life than those from the lower canopy. Shelf life was correlated with fruit color at harvest.

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M. Chérif, J.G. Menzies, D.L. Ehret, C. Bogdanoff and R.R. Bélanger

Two experiments were conducted in separate locations, one at Université Laval in eastern Canada (Québec) and one at the Agassiz Research Station in western Canada (British Columbia), in an attempt to determine the effectiveness of soluble silicon (Si) against cucumber root disease caused by Pythium aphanidermatum Edson. Long English cucumber (Cucumis sativus L. cv. Corona) plants were grown either in a standard nutrient solution or in nutrient solutions supplemented with 1.7 mm (100 ppm) Si and inoculated or not with the pathogen. Supplying the solutions with 1.7 mm Si significantly reduced mortality and disease symptoms attributed to infection by P. aphanidermatum. Grown in presence of Si, plants infected with P. aphanidermatum showed a significant increase in yield, marketable fruit, and plant dry weight compared to Si-nonamended and infected plants. These beneficial effects were observed under both experimental conditions. The fruit yield of noninoculated plants was not affected by the presence of Si in the Agassiz experiment. However, Si-amended control plants were more productive in the experiment conducted at Laval, apparently because of contamination problems, which indicates that Si beneficial effects are most likely related to disease management.

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W.C. Lin, G.S. Block, S. Chen and D.L. Ehret

In commercial production of greenhouse cucumber, moderate water stress is often undetectable until plants show severe wilting. The purpose of this study was to establish a noncontact, early detection method for such moderate stress before visual wilting takes place. An infrared imaging system including an infrared camera, a personal computer, and necessary image processing software was placed in a greenhouse with the camera elevated and viewing the plant canopy. Selected plants, each in a bag of sawdust growing medium, were subjected to water stress by removing irrigation tubes from the growing medium. The infrared images obtained from a crop canopy displayed an increase in foliar temperature of stressed plants, which were located among normally watered (control) plants in the same greenhouse. Increased foliar temperatures of stressed plants occurred 1 to 3 days before wilting was observed. When visual wilting occurred, the stress treatment was stopped and irrigation was resumed within the same day. Cucumber plants showed no crop loss after one cycle of moderate stress. Repeated moderate stress caused yield loss. The potential applications of this nondestructive, noncontact detection method in plant science research and in commercial greenhouse production will be discussed.