ウメ果実の樹上及び収穫後の成熟

Abstract

Ripening characteristics of mume (Japanese apricot, cv. Nanko) fruits on and off the tree were investigated from the pit-hardening stage to the fully-ripe stage. To study ripening off the tree, fruits were picked at four stages of development and stored at 20°C.Climacteric patterns were observed in the carbon dioxide production rate of fruits both on and off the tree. In fruits ripened off the tree, earlier onsets and a higher maximum values of the climacteric were observed as harvesting time was delayed.The rate of ethylene production in attached fruits remained below 0.1μl/kg•h until the first yellow coloring appeared on the skin surface, and then increased rapidly to reach a maximum value above 500μl/kg•h at the fully-ripe stage. A similar rise in ethylene production occurred during ripening in detached fruits, in which case production began earlier and reached a higher peak value as harvesting time was delayed.The free abscisic acid content of attached fruits increased rapidly after the skin color yellowed. In detached fruits, abscisic acid also increased once, after harvest, and then decreased, but levels were considerably lower than those in fruits ripened fully on the tree.Sucrose content showed a steady increase until fully-ripe stage in fruits on the tree, and a similar rise in detached fruits, to a lesser extent. The concentrations of fructose, glucose, and sorbitol in attached fruits also increased as the fruit ripened, but in detached fruits concentrations slowly declined after harvest.A linear increase in citric acid and, contrarily, a linear decrease in malic acid was found in attached fruits from the pit-hardening stage to the fully-ripe stage, which caused a slight change in total acidity. Similar trends were observed in detached fruits, where citric acid increased until some time after picking, whilemalic acid was steadily declined during ripening.It seems that the internal preparations for ripening of mume fruits are complete at the pit-hardening stage, after which detached fruits show a ripening pattern similar to that which occurs on the tree, and that ripening is more rapid as har vesting time is delayed.