Responses of apple tree cultivars to drought: carbohydrate composition in the leaves

The changes in the composition of carbohydrates in the leaves of several apple cultivars were investigated during fruit development in an intensive plantation and in a model experiment. Analytical measurements were performed on leaves collected from the eastern, western, and southern sides of trees four times: on days 57, 73, 99, and 120 after flowering. Simultaneously, the shoots collected from these varieties were exposed to mild, moderate, and severe water stress induced by polyethylene-glycol solution, modeling drought. Under short-term drought, a close significant correlation (R = 0.8348) was found between the degree of leaf rolling and the carbohydrate (glucose + fructose) content 73 days after flowering. During mild drought, water-intensive cultivars exhibited significant leaf rolling and high accumulation of carbohydrates, while those with moderately rolled leaves contained less glucose and fructose. During severe drought, it is the sucrose content of leaves that can be considered a stress indicator, while during temporary dry periods, it is the changes in the glucose + fructose content of leaves. The early stage of slow fruit development was more suitable for screening the drought tolerance of apple trees based on the changes in morphology and the carbohydrate composition of the leaves. The results can be used to select apple trees with good adaptability to drought in breeding programs.