Effects of Day Length and Temperature on the Vegetative Growth and Flower Bud Differentiation of Satsuma Mandarin

Abstract

Effects of day length and temperature on the vegetative growth and flower bud differ- entiation of one-year-old satsumas on trifoliate orange were observed in a growth chamber and under field conditions during the growing (Experiment 1) and dormant seasons (Experiment 2). Room temperatures were kept constant at 15, 20 and 25t. Photoperiod treatments were 8 (short day : SD) and 16 hours (long day: LD) and natural day length (ND). 1. Short day treatment from sprouting time depressed shoot growth in spring and summer. Shoot growth increased with 16-hour photoperiods. The trees at 15 and 20°C sprouted flower buds on the spring shoots in September to October regardless of day length. Many flower buds appeared following the 8-hour photoperiod in the field, after defoliating and transferring the trees into 25°C room in late October. The trees on long days produced more fresh weight than did those on short days. 2. Sixteen-hour photoperiods during 2 or 3 months from late October decreased flower buds on spring shoots. Short days tended to increase flower bud differentiation. More flowers were produced in 15°C room than in the field.