Seasonal variations in fruit characteristics and relationships among them in keraji (Citrus keraji)

Seasonal variations in fruit characteristics and relationships among them in keraji (Citrus kerajl), which is a local cultivar mainly grown on Kikai-jima island, Kagoshima prefecture were studied. Although the fruit of Keraji was inferior to that of satsuma mandarin (C. unshiu) in terms of coloration of skin, the titratable acidity of Keraji was almost the same as that of 'Okitsu wase' which is an early ripening clone of satsuma mandarin. The Brix value of Keraji which was slightly higher than that of 'Okitsu wase', increased until early February. Sugars in the juice of Keraji consisted of fructose, glucose and sucrose. Sucrose was the predominant sugar component, followed by glucose and fructose in mature fruit, and this composition was similar to that of many citrus accessions. On the other hand, the juice of Keraji showed characteristic acid constituents. The content of citric acid in juice decreased rapidly during the growth period, while the content of malic acid increased gradually from October. Consequently, the malic acid content was approximately 40 % of the citric acid content in January and February. The contents of polymethoxy flavones (PMFs) which are characteristic phytonutrients of citrus in the juice of Keraji was almost the same as those of Ponkan (C. reticulata), one of the species with the highest PMF contents. On the other hand, the PMF contents in the peel were lower than those of Ponkan and Shiikuwasha (C. depressa). A positive correlation was revealed between the number of leaves, diameter of the peduncle and rind texture, and fruit weight. Generally fruits with coarse rind and good coloration display a low and high Brix value, respectively. The fruit weight was negatively correlated with the titratable acidity, but not significantly with the Brix value. The correlation between the number of seeds per fruit and the fruit weight was not significant.