The effect of temperature on flower-bud formation in apple including some morphological aspects

Abstract

To study the effect of temperature on flower-bud formation, shoot growth and bud morphogenesis of apple ( Malus domestica Borkh.), three-year-old trees cv. Summerred were exposed to six temperature treatments in two successive periods of about 6–7 and 12 weeks, starting at full bloom: (a) 13 and 13 °C; (b) 13 then 20 °C; (c) 20 and 20 °C; (d) 20 then 27 °C; (e) 27 and 27 °C; and (f) 27 then 13 °C. Shoots were clearly longer at 20 than at 13 °C throughout the season, but a further increase to 27 °C had little effect. Increasing the temperature 6–7 weeks after bloom also stimulated growth considerably. Lowering the temperature from 27 to 13 °C stopped growth completely. Raising the temperature either from full bloom or from 6–7 weeks after bloom favoured flowering on spurs as well as one-year-old shoots but the effect was most pronounced in the 13–20 °C range. Very few flowers were formed in the 27–13 °C treatment. Flower quality based on the number of well-developed flowers per cluster tended to decrease with increasing temperature. Bud dissection showed that flower-bud formation was clearly delayed in the 13-13 treatment. Increasing the temperature from 13 to 20 °C 6–7 weeks after bloom advanced flower-bud formation but the increase from 20 to 27 °C at that time gave some delay. The number of nodes in buds when generative development just started was highest in spur buds. The effect of temperature on node number did not show any consistent pattern.