Drought Tolerance of ‘Fuji’ Apple Trees Grafted onto G, CG, or M Series Rootstocks: Growth and Physiology

In this study, we assessed the drought tolerance of 1-year-old apple (Malus domestica Borkh.) treesexposed to extreme water stress, focusing on growth and physiological responses. After grafting‘Fuji’ variety onto M26 and M9 rootstocks or Cornell-Geneva rootstocks (G11, G202, G214, G935,CG4814, and CG5087), the grafted plants were planted in 17-L pots and managed in a greenhouse. After irrigation was stopped, soil water potential dropped to about –700 hPa in 12 days. The leafwater potential and tree vertical growth rate of drought-stressed trees decreased dramatically, andthe decreased growth rate of the G202, G935, and M26 trees, which generally produced a large leafarea, was considerable. Trunk cross-sectional area and leaf area of all trees under drought stresswere reduced by almost 50% or more than 60%, respectively. Drought-stressed trees were subjectedto control-level irrigation during the recovery of about 11 days, but their leaf water potential still didnot fully recover to the control level. Photosynthesis-related parameters also showed a substantialdecrease as the soil water potential changed, but the difference among trees was not noticeable. Fine root (