Development of early watercore in 'Orin' apples grown in warmer regions and its physiology

The occurrence of watercore in 'Orin' apples (Malus pumila Mill. var. domes tica Schneid.) was prevalent from late August to late September; there was a significant correlation between watercore rating and maximum fruit temper ature during late August. The watercore occurred in immature apples long be fore the increase of ethylene and 1-aminocyclopropane-1-carboxylic acid (AC C), indicating that the watercore observed in this study was early watercor e. Membrane permeability increased from mid-August to mid-September and sho wed a significant correlation with watercore. The degree of watercore durin g late August was significantly correlated with flesh firmness, soluble sol ids content (SSC), total sugars, fructose, glucose in the inner flesh, and sorbitol but not with titratable acidity, starch, and sucrose. The seasonal changes in sorbitol content paralleled the incidence of watercore; the coe fficients of correlation between them were 0.881 and 0.827 for the inner an d outer flesh tissue, respectively. These results indicate that the changes in physiological factors such as membrane permeability and sorbitol conten t in the fruit during summer play an important role in inducing early water core in apples. We propose that the physiological mechanism of early waterc ore development in immature apples is similar to that of high temperature-i nduced watercore during maturation but differs from that of low temperature -promoted late watercore.