Effects of Air and Soil Temperature on Vegetative Growth and Flower Bud Differentiation of Satsuma Mandarin Trees

Abstract

One-year-old satsuma mandarin (Citrus unshiu Marc. cv. Okitsu Wase) trees budded onto trifoliate orange rootstocks were subjected to different soil temperature (15, 20, 25 and 30°C) and air temperature treatments (25°C in Experiment I, and 15 and 30°C in Experiment II) for 6 or 7 months. The effects of air and soil temperatures on vegetative growth and flower bud differentiation were investigated. The number of flushes and total length of the shoots increased with rising soil temperatures. When soil temperatures were above 20°C, the number of flushes at an air temperature of 15°C was less than at 30°C. The length of spring shoots at an air temperature of 15°C was longer than at 30°C. However, due to the trees at air temperature of 30°C having more growth cycle flushes, the total length of the shoots did not differ among treatments. The dry weight of the trees increased with increases in both air and soil temperatures. Both low air and low soil temperatures affected flower induction greatly. At an air temperature of 30°C, flower buds developed only at soil temperatures of 15 and 30°C. At an air temperature of 15°C, flower buds developed even when the soil, temperature was 30°C. Trees with air/soil temperatures of 25/30, 30/25 and 30/30°C did not bear any flower buds. The effects of temperature on mineral nutrient content were slight. The roles of soil and air temperature on vegetative growth and flower formation are briefly discussed.