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The study was conducted to determine the effects of 2,4-DP and GA₃ on ripening of ´Tsugaru´ apples, with special emphasis on the changes in quality attributes. Increase in CO₂ and ethylene evolution as well as skin redness indicated that the fruits treated with 2,4-DP alone and in combination with calcium acetate ripened 20 and 10 days earlier, respectively, than those with GA₃ and none. Fruit size increased by GA₃, and decreased by 2,4-DP mixed with calcium. Treatment with 2,4-DP was characterized by the enhanced loss of fruit firmness. Starch content decrease and soluble solids content increase were faster in those fruits treated with 2,4-DP alone than any others. Fructose concentration was about 55% of total soluble sugars at harvest. Chemical sprays did not affect concentrations and proportions of fructose, glucose, sucrose, and sorbitol in the fruits. However, GA₃ tended to reduce the concentrations of sucrose and glucose. Malic acid was over 60% of total organic acids in fruit. Titratable acidity and malic acid concentration declined much faster when treated with 2,4-DP alone. A higher concentration of malic acid was found in those fruits treated with GA₃.
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