Studies on cold injury of citrus sinensis cultivar fukuhara orange fruit 2. factors related to tolerance of flesh freezing
Bulletin of the Fruit Tree Research Station Series D (Kuchinotsu) (5): 67-74
Seven year old potted trees were incubated in a cold environment. The time required to freeze, supercooling temperature and freezing temperature in the fruit were recorded with a resistance thermometer. The data obtained from the experiments were adapted to multiple regression analysis, selecting the best regression equation by a stepwise regression procedure. Seasonal changes in the freeze tolerance were examined. The time required to freeze was directly related to fruit weight, the lowest temperature, soil moisture and Brix of the juice. The time was longer for larger fruit size, decrease in temperature at supercooling, decrease in soil moisture and increase in Brix. The supercooling point was related to the freezing point and the lowest temperature. The freezing point was related to soil moisture, minimum temperature, Brix of the juice and fruit diameter; it became lower with an increase in soil moisture and Brix of the juice and with decrease in fruit size. For fruit having a higher concentration of citric acid in its juice, freezing was delayed and the supercooling point was lowered. The supercooling point and the freezing point gradually lowered with the maturity of the fruit; however, the time required to freeze did not change. More dry juice sacs occurred when matured fruit was frozen in April.