Studies On Physiological Mechanism Of Grafting Superiority In Cucumber

Cucumber (Cucumis sativus L.) is one of the important vegetables that are enjoyed by worldwide people. For cucumber's system of root, capacity of absorbing water and fertilizer and resistance to all kinds of stresses are poor, high yield and all-year-round supply of cucumber are very difficult to realize. With application and development of grafting technology for cucumber, the problems have been partly solved, especially, winter planting of cucumber. But grafting theories have many deficiencies, many studies were focused on function of grafting, and studies on physiological mechanism of grafting superiority were rarely reported. Making sense of the mechanism can provide convincing theoretical foundation for application and development of grafting technology of cucumber.Using black seed pumpkin {Cucurbita ficifolia Bouche) as root stock, and two cucumber cultivars JinlU21-1 and Jinyan 4 as scions, grafting was made to compare the differences in photosynthetic parameters, leaf nutrient element contents, activities of membrane protective enzymes and MDA contents, leaf GA and ABA contents, and leaf soluble protein components between grafted and self-root cucumber, and physiological mechanism of grafting superiority was discussed. The results showed that morphological indexes at different stages of grafted cucumber were significantly higher than those of self-root cucumber. The individual plant yield of grafted cucumber was significantly higher than that of self-root cucumber. Grafting superiority in individual plant yield of Jinyan 4 was better than that of Jinlu21-l. Disease index and disease percentage of wilt, virus, downy mildew and botrytis of grafted cucumber were lower than those of self-root cucumber. Accompanied with senescence of leaf, photosynthetic rate and stomatal conductance decreased gradually, at the same time, intercellular CO2 concentration decreased in first stage and rised in late stage, but photosynthetic rate, stomatal conductance and intercellular CO2 concentration of grafted cucumber were significantly higher than those of self-root cucumber at different stages. Grafting superiority in photosynthetic rate of Jinyan 4 was better than that of Jinlu21-1. Leaf N P K, Ca and Mg contents of grafted cucumber were significantly higher than those of self-root cucumber. With senescence of leaf, soluable protein contents in leaves of grafted and self-root cucumber decreasedgradually, but soluable protein contents in leaves of grafted cucumber were higher than those of self-root cucumber. With the increase of leaf age, SOD and CAT activities of grafted and self-root cucumber decreased gradually, at the same time, POD activities of grafted and self-root cucumber decreased in last stage as well. But SOD, CAT, and POD activities of grafted cucumber were significantly higher than those of self-root plant. MDA contents in leaves of grafted and self-root plant both rised, but MDA content of grafted cucumber was significantly lower than that of self-root plant. Leaf GA and ABA contents at various measuring stages of grafted cucumber were significantly different to those of self-root cucumber. ABA content at the last measuring stage of grafted cucumber was significantly higher than that of self-root cucumber. ABA/GA values of leaves of grafted cucumber were significantly higher than those of self-root cucumber at various measuring stages. Soluble proteins extracted from the leaves of grafted and self-root cucumber were analyzed using the technique of two-dimensional polyacrylamide gel electrophoresis. The results indicated that there were one to two additional protein spots from grafted cucumber.