| Cucumber (Cucumis sativus L.) is an important vegetable crop. It likes warm and wet climate, it is usually subject to high temperature and rainy weather damage when cultivated in summer at south areas of our country. Therefore, studies on heat and waterlogging tolerance of cucumber are extremely necessary. Howover, few studies has been done owing to the strict region of cucumber. By screening the appraisal indices of heat and waterlogging tolerance in cucumber, we can use them to enhance the efficiency of identifying and screening materials and cultivars, to serve the adversity-resistance breeding and production.The main results are as follow,1. Studies on heat toleranceIn order to find the best method or reliance index of appraising the degree of heat tolerance of cucumber, ten cucumber varieties were treated with high temperature at different developmental stages in this experiment. By studying the physiological and biochemical indexes of cucumber under high temperature and calculating the correlativity among these indexes, we look for convenient and reliable indexes to identify heat tolerance of cucumber materials.The experimental result shows as follows. There are some differences of heat tolerance among cucumber varieties at different growth duration. The cucumbers whose seedlings were treated with high temperature expressed the following tendency of the increase of the permeability of plasma membrane, MDA content, free proline content and SOD activity. After treated with high temperature, the yield of cucumber decreased.The permeability of plasma membrane, free proline content, SOD activity and yield under high temperature may be used as the appraised indexes of cucumber heat tolerance at seedling stage.In order to select out the heat tolerance material of the cucumber, we had compared that the heat tolerance in the field and the heat tolerance of the cucumber seedling under 40℃for 72h in different ecotype cucumber cultivars. The results shown, it was identified that ten cultivars were heat tolerance. That is E, B, A, D, C, Rebao NO.3, Taiwanlvxiu, Nairexianfeng, jinyou NO.4, etc.2. Studies on waterlogging toleranceFour cucumber lines were pot-cultured and then waterlogged in 4 leaf stages and were used for studying mechanism of antioxidant defense system in cucumber seedling subjected to waterlogging stress. The effect of waterlogged stress on damage index of seedling leaf, physiological and biochemical characteristics of cucumber were studied. The results showed that the true leaf became yellow and lack of chlorophyll after waterlogged. The aerial root was produced in seedling stem after waterlogged stress as to adapt to the stress evolution. SOD activities of leaf of four cucumber lines decreased at beginning and then increased, until to approach the control. It demonstrated that seedling of cucumber possessed a significantly larger self-regulating ability. In contrast, POD activities of all were higher than the control. CAT activities decreased at beginning and then increased. Free proline contents of all treatment after waterlogging stress was lower than the control. MDA contents of all were higher than the control after submergence, the MDA contents in tolerance increased firstly, then decreased.3. Studies on heat and waterlogging toleranceFour cucumber lines were pot-cultured and then waterlogged in 4 leaf stages and were used for studying mechanism of antioxidant defense system in cucumber seedling subjected to heat and waterlogging stress. The effect of heat and waterlogged stress on damage index of seedling leaf, physiological and biochemical characteristics of cucumber were studied. The results showed that the true leaf became yellow and lack of chlorophyll after heat and waterlogging stress. Free proline contents, MDA contents and POD activities of all treatment after heat and waterlogging stress was increasing gradually. SOD activities increased at begin, then decreased and increased at last. CAT activities increased at begin, then decreased.
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