Evaluation of Salt Resistance of Six Apple Rootstocks

Apples (Malus domestica Borkh) are important fruits in China; however, salt stress is severe in northern regions, and the key to plant resistance to salt stress lies in the rootstock. Therefore, it is necessary to explore rootstocks with strong salt resistance for the development of the apple industry. This study used tissue culture seedlings of six apple rootstocks, namely, '71-3-150', '54-118', 'M9T337', 'GM256', 'ML176', and 'ML2', as experimental materials. The seedlings were treated with a medium containing 150 mM NaCl, and the physiological indicators and related gene expression responses of several rootstocks were studied after salt stress. The results showed that salt stress affects the growth of both the aboveground and underground parts of plants. Through physiological indicators and the related gene expression responses of rootstocks, it was observed that salt stress significantly increased Na⁺ contents in different rootstocks. Simultaneously, the activity of various antioxidant enzymes and the expression levels of related genes also increased. In summary, by analyzing the parameters of various physiological indicators, it can be concluded that among the studied rootstocks, the '71-3-150' and '54-118' rootstocks have the strongest resistance to salt stress, while the 'M9T337' and 'GM256' rootstocks exhibit moderate resistance, and the 'ML176' and 'ML2' rootstocks have the weakest resistance.