Fruit Thinning and Physiological Disorders in Citrus Variety ‘Harumi’

Citrus ‘Harumi’ is a mandarin-type cultivar and shows a wide range of fruit size, which affects fruit quality such as sugar and acid contents. In citrus, fruit size also affects the degree of physiological disorder which become a big problem during storage. Thus, making fruit with equal and appropriate size is very important. Fruit thinning is one of the most important techniques to adjust fruit size by controlling the fruit number. Basically, fruit thinning has been conducted using a criterion based on leaf and fruit ratio (L/F) or fruit number per canopy volume. In this review, several thinning criteria for ‘Harumi’ and other citrus varieties are compared, and the pros and cons are discussed. In some citrus varieties, storage is necessary to adjust shipping time. During the storage, some physiological disorders occurred in peel, flesh and whole fruit. The occurrence of physiological disorders was influenced by citrus variety, fruit size and environmental conditions during storage. In ‘Harumi’ which is classified to easy-peeling variety, small fruit showed serious weight loss and peel wrinkle, while rind puffing and dehydration of flesh were big problems in large fruit during storage. Polyethylene (PE) bag wrapping has been used to decrease the fruit weight loss and to prevent the occurrence of some physiological disorders in tightskin citrus varieties. However, the influences of PE wrapping on easy-peeling citrus is unclear. In this study, the researches on storage conditions, feature, and cause of physiological disorders during storage are also reviewed, and the effects of PE wrapping are discussed to improve storage condition in ‘Harumi’.