Effects of Grafting Patterns on Photosynthetic Characteristics and Antioxidant System of Cucumis Melo Seedlings under Low Temperature Stres

[Objective] The study aims to explore the physiological mechanism of different grafting patterns in alleviating the low temperature stress of melon (Cucumis melo L.) seedlings, in order to provide a theoretical basis for selecting appropriate grafting patterns to improve the resistance of melon to low temperature. [Methods] Taking the thick and thin skin melon varieties as scions, respectively, and the white seed pumpkin as a rootstock, with the self-rooted melon seedling as control, the effects of double root, adhering, and attaching grafting patterns on the photosynthetic pigment content, photosynthetic gas exchange parameters, cell membrane permeability, and antioxidant enzyme activity of leaves of melon seedlings were studied under three treatments, including before low temperature (15 ℃/10 ℃), low temperature, and after low temperature treatment (rewarming treatment). [Results] (1) The photosynthetic pigment content and photosynthetic gas exchange parameters of leaves of the grafted seedlings of various melon varieties were decreased under low temperature treatment; these physiological parameters were increased after rewarming treatment, among which the attaching grafted seedling had the lowest decrease and the highest increase. (2) The relative conductivity, malondialdehyde content, hydrogen peroxide content, and superoxide anion production rate in leaves of the grafted seedlings of all melon varieties were increased under low temperature treatment, and were decreased under rewarming treatment, among which the attaching grafted seedlings had the lowest increase and the highest decrease. (3) The activities of superoxide dismutase, peroxidase, and catalase in leaves of the grafted seedlings of all melon varieties were increased under low temperature, and were increased under rewarming treatment, and the attaching grafted seedlings had the most significant increase. [Conclusion] The three grafting patterns enhance the activities of antioxidant enzymes of thick-skinned and thin-skinned melon seedlings under low temperature stress and rewarming, and effectively reduce the accumulation of reactive oxygen species, maintain the photosynthetic capacity of seedlings, and improve low temperature tolerance of seedlings. The attaching grafting has the best performance.