The drought resistance of eight commonly used apple rootstocks under natural drought conditions was examined to provide clues for the selection, promotion, and utilization of drought-resistant apple rootstocks. The ultrastructural differences and physiological and biochemical characteristics of the leaves of eight apple rootstocks under drought stress were observed. The index changes were used to rank drought resistance by the membership function method comprehensively. The results showed that the leaf thickness, palisade tissue thickness, sponge tissue thickness, net photosynthetic rate, and chlorophyll content were significantly higher in 'Fupingqiuzi' than those of other rootstocks at various stress conditions. The leaf water content and water use efficiency of 'Qingzhen 1' were significantly higher than those of other rootstocks under different stress conditions. The root vigor of 'B.9' was significantly higher than that of other rootstocks. The results of membership function analysis showed that the drought resistance of different rootstocks was in the order: 'Fupingqiuzi' > 'Qingzhen 1' > 'B.9' > 'MM.111' > 'GM256' > 'MM.106' > 'M.26' > 'M.9-Nic29'. 'Fupingqiuzi' had the strongest drought resistance, and 'Qingzhen 1' and 'B.9' were also relatively drought-resistant. These rootstocks can be used as raw materials for drought-resistant apple rootstock breeding and are propagated and utilized in arid areas.
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