Effect of goji berry rootstock grafting on growth and physiological metabolism of tomato under high-temperature stress

In this study, the effects of goji berry (Lycium barbarum L.) grafting on tomato growth, photosynthesis, antioxidant metabolism and osmoregulatory substances under high-temperature stress were studied with black goji berry and red goji berry as grafting rootstocks and 'Sufen 14' tomato as scions. It was found that under room temperature conditions, the growth of goji berry grafted tomato plants was inhibited compared to self-rooted tomato plants, and goji berry rootstock grafting could alleviate the adverse effects of high-temperature stress on plant height, stem diameter, and root activity. After 21 days of high-temperature stress, the heat damage index of the self-rooted tomato plants was greater than 0.6, while the heat damage index of the grafted seedlings of black goji berry and red goji berry were medium high-temperature tolerance and strong high-temperature tolerance, respectively. Under high-temperature stress, chlorophyll a (Chla), net photosynthetic rate (Pn) and transpiration rate (Tr) of tomato were significantly increased by grafting of goji berry rootstock. The Pn of tomato was significantly increased by grafting of black goji berry rootstock than that of grafting of red goji berry. Leaf stomatal conductance (Gs) and intercellular CO2 concentration (Ci) were significantly decreased by grafting of goji berry rootstock. The maximum photochemical efficiency of PSII (Fv/Fm), actual photochemical efficiency of PSII (Phi PSII) and regulated energy dissipation in PSII (Phi NPQ) were significantly increased by goji berry grafting under high-temperature stress. Under high-temperature stress, the contents of proline, soluble sugar, soluble protein and antioxidant enzyme activities of grafted tomato leaves were significantly increased, while the levels of hydrogen peroxide (H2O2) and malondialdehyde (MDA) were significantly decreased. The activities of ascorbic acid (APX) and superoxidase (SOD) in grafted plants of black goji berry rootstock were significantly higher than those of grafted plants of red goji berry rootstock. The catalase (CAT) and peroxidase (POD) activities of red goji berry rootstock grafted plants were significantly higher than those of black goji berry rootstock grafted plants. The above results showed that the grafting of goji berry rootstock reduced the oxidative damage induced by high-temperature stress, promoted photosynthesis of tomato plants, and improved the heat resistance of tomato plants by regulating the antioxidant defense system and osmoticregulatory substances. Moreover, the heat resistance of black goji berry rootstock grafted to tomato was better than that of red goji berry rootstock grafted plants.