Determination of morphological, physiological and biochemical responses of different clonal rootstocks and jeromine apple variety grafted on these rootstocks under drought stress

Apples are among the world's most economically important fruits, and drought stress is a significant factor limiting the development of the global apple industry. This study evaluated the morphological, physiological, and biochemical responses of three different clonal apple rootstocks and the Jeromine apple variety grafted onto these rootstocks to drought stress. In the study, the control group was grown under full irrigation (100% field capacity), while the other group plants were left without water." According to morphological findings, rootstocks MM111 and MM106, especially in combination with Jeromine, maintained high levels of growth parameters such as shoot length, shoot diameter, leaf area, and root biomass under drought. While the MM111/Jeromine combination achieved the highest shoot length in both years (23.23-20.50 cm), the M9 and M9/Jeromine combinations experienced significant growth losses under stress conditions. In terms of root fresh and dry weight, rootstock MM111 stood out with its robust root development, while rootstock M9 exhibited the weakest root performance. Physiological assessments were conducted on parameters sensitive to drought stress, such as leaf relative water content (RHWC), specific leaf weight, and membrane permeability. The MM106/Jeromine and MM111/Jeromine combinations were the most successful in maintaining intraleaf water balance and cell membrane integrity. M9 rootstock was determined to be the most sensitive to stress, with the highest water loss and increased membrane permeability. MM111 rootstock maintained its biological integrity by best preserving membrane stability. Biochemical analyses measured the enzymatic defense responses of plants against oxidative stress. Increases in superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activities were observed with drought treatments; these increases varied among combinations. The MM106/Jeromine combination achieved the highest SOD and POD increases in both years, providing the most active defense against oxidative damage. On the other hand, the MM111/Jeromine combination was particularly effective in reducing intracellular hydrogen peroxide (H₂O₂) levels, yielding the highest values in CAT activity. M9 and M9/Jeromine were the weakest groups in coping with stress, both in terms of enzyme activity and H₂O₂ accumulation. This study highlights the importance of selecting a rootstock and cultivar combination with high stress tolerance to ensure the sustainability of apple production in regions with limited water resources. MM111 and MM106 stand out as rootstocks tolerant to drought stress; these rootstocks are recommended for the sustainable cultivation of the Jeromine apple variety in arid and semiarid climates.