Study on Relationship Between Physiological Changes and Chilling Tolerance in Grafted Watermelon Seedlings Under Low Temperature Stress

Compared with own-rooted watermelon, the influence of different rootstocks on chilling tolerance of grafted watermelon seedlings and its physiological mechanisms were studied. The results showed that grafting increased the chilling tolerance. Compared with own-rooted watermelon seedlings, the grafted watermelon seedlings had lower chilling injury index, lower electrolytic leakage (%), lower MDA content, higher chlorophyll, proline content and higher activities of superoxide dismutase, ascorbate peroxidase and dehydroascorbate reductase in leaves under low temperature stress. There was a considerable difference of chilling tolerance among different grafted watermelon seedlings due to the difference of rootstock chilling tolerance. The grafted seedlings with stronger chilling tolerance had lower electrolytic leakage (%), lower MDA content, higher proline content and higher activities of superoxide dismutase, ascorbate peroxidase, dehydroascorbate reductase in leaves than those of grafted seedlings with weaker chilling tolerance. Therefore, chilling tolerance may be related to higher antioxidative ability and membrane stability in the plants. The chilling tolerance of grafted seedlings could be properly evaluated by comprehensive physiological indexes but not a single physiological index.