チュウゴクナシ‘鴨梨’果実の樹上および収穫後の成熟特性

Abstract

Ripening characteristics of the Chinese pear 'Yali', Japanese pear 'Nijisseiki', and European pear 'La France' on and off the tree were compared.Respiration rates of all three kinds of pear fruit on the tree increased slightly during the late stage of maturation. A typical climacteric pattern was observed in stored fruit of 'Yali' and 'La France', but not in those of 'Nijisseiki', independent of their maturity.Ethylene production by intact fruit was detected just before the 'Yali' fruit abscised and during the late mature stage of 'La France', but none was detected in 'Nijisseiki' fruit even at the overripe state. Ethylene production in the stored fruit of 'Yali' and 'La France' showed a marked climacteric pattern which was accompanied by corresponding changes in 1-aminocyclopropane-1-carboxylic acid (ACC) and the ethylene-forming enzyme (EFE) activity. Stored 'Yali' fruit evolved a large volume of ethylene, reaching a maximum of 380 nl/g•hr. The rate of ethylene production at the climacteric peak was progressively lower as the harvest date was delayed. Contrarily, stored 'Nijisseiki' fruit disclosed an unusually high ACC content but a low level of EFE activity while evolving no ethylene.A drastic decline in starch and a slight increase of sugar were commonly observed in the three pear cultivars during their maturation process. However, their composition of sugars differed. In 'Yali' and 'La France', fructose was the predominant sugar throughout the maturation and ripening stages, whereas, in a ripe 'Nijisseiki' fruit, sucrose was the dominant sugar.Malic acid was the predominant acid in the three pear cultivars. No sharp changes in acid content occurred in 'Yali' and 'Nijisseiki' fruits while they were maturing, but malic acid content increased briefly in 'Yali' fruit as it ripened. Malic acid level in 'La France' increased steadily while the fruit matured but the level declined rapidly as the fruit ripened.During maturation on the tree fruit firmness decreased gradually in 'Yali' and 'Nijisseiki' but rapidly in 'La France' during maturation. 'Yali' fruit remained relatively firm during storage but those of 'La France' softened rapidly, whereas those of 'Nijisseiki' softened gradually. We found that 'Yali' fruit retained their firmness even though they produced voluminous amounts of ethylene.