Abstract：Drought is one of the vital factors that affect the apple (Malus × domestica) production in China, while the ability of drought resistance of stock directly affects the scion growth and development, fruit yield and quality. In this study, seven apple dwarfing stocks from SH series (SH1, SH6, SH40), M series (M26, M9-T337) and G series (GX, CG24), grafted on base rootstock Malus hupehensis var. pingyiensis respectively, were used for evaluation on drought resistance. After 40 d drought stress, growth and physiology indices were analyzed comparatively, and the ability of drought tolerance was ranked by comprehensive evaluation of subordinate function value (SF). Those results showed that the trunk growth rate (TGR) for GX, CG24 and M9-T337 was worst restricted, whereas SH6 performed the highest TGR both in control and water stress plants, and the later up to 80.6% contrast to the control. Besides, GX and M26 got the largest drop on transpiration rate (Tr) than others under drought stress, which decreased 50% than that of control. Net photosynthetic rate (Pn) in M9-T337 and SH6 was affected non-significantly under drought stress, whereas the GX showed the lowest Pn than other stocks. For the detection on leaf relative conductivity, the significant elevations under drought stress occurred in GX and CG24, and SH6 showed the most stability than others. Results on leaf water potential suggested that SH series dwarfing stocks had higher water potential whether in well-watered or drought conditions, whereas GX suffered series drop. Collectively, based on comprehensive evaluation of SF for above five indexes detected, drought resistance evaluation were conducted and ranked as follows: SH6＞SH40＞M9-T337＞SH1＞M26＞CG24＞GX. In following comparing analysis between SH6 and GX, four antioxidases including superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and dehydroascorbate reductase (DHAR) showed higher activity levels in SH6 than those of GX, and response actively with drought stress process was observed in SH6 but none in GX. In addition, cluster analysis of gene expression levels in SH6 and GX samples showed that 12 genes were divided into two groups. The first group, including 6 genes (DREB1A, DREB2A, DREB2B, DREB2C, DREB6 and ZAT10) expressed at higher levels in GX samples, whereas the other group expressed mainly in SH6 samples, from which 4 genes (SOD1, APX1, CAT1 and DHAR2) were belong to antioxidase families, suggesting higher levels of antioxidant enzyme activities may contribute to drought resistance. This study provides a theoretical reference for the application of apple dwarfing stock and drought-resistant breeding.
