Effects of Gibberellic Acid Spray and Temperature in Summer and Autumn on Shoot Sprouting and Flower Bud Differentiation of Satsuma Mandarin

Abstract

ウンシュウミカンの新梢発生と花芽分化に及ぼす夏秋季のジベレリン散布と温度の影響 One-year-old potted satsumas (cv. Okitsu Wase) on trifoliate orange rootstocks ere grown at 15, 20 and 25°C in a growth chamber and in the field for 6 months from mid-June. They were sprayed twice each month with 100ppm of gibberellic acid on 11th and 26th from June to November. Effects of gibberellic acid sprays and temperatures in summer and autumn on shoot sprouting and flower bud differentiation were observed. Moreover, after defoliating and transferring the trees into 25°C room in mid-December, flushing of flowers and vegetative shoots was investigated.1. Gibberellin sprays promoted flushing of summer shoots on spring ones at 25°C and in the field. The spring shoots without summer flushes increased in diameter as spraying times were earlier and temperatures were higher.2. After defoliating and transferring the trees into 25°C room in mid-December, a smaller number of flowers developed in higher temperatures. Earlier sprays of gibberellin strongly depressed development of flower buds. Even the latest spray in November decreased the number of flushes below a quarter of the number of flowers in the non-sprayed trees.3. On the defoliated trees after transferring into 25°C room in mid-December, more shoots flushed at lower temperature treatments. Effects of gibberellin sprays were different between temperature treatments. Earlier sprays at 15°C produced more shoots. However, later sprays at 25°C decreased flushing of shoots. In the field, the fewest number of shoots were observed in the non-sprayed trees. Gibberellin sprays promoted flushing of more shoots in and after September than in June to August.