Temperature affects Chrysanthemum flower characteristics differently during three phases of the cultivation period

The sensitivity to temperature of the number of flowers per plant including flower buds (NFPP), flower size, position and colour was investigated in cut chrysanthemum (Chrysanthemum morifolium cv.'Reagan Improved'). Plants were grown either in a glasshouse at constant 24 h mean temperatures throughout cultivation (17 degrees C or 21 degrees C), or in growth chambers at 32 different temperature combinations (from 15 degrees C to 24 degrees C). The latter temperature combinations were applied by dividing the cultivation period into three sequential phases: long-day period (phase I), start of short-day period to visible terminal flower bud (phase II), and end of phase II to harvest stage (phase III). All flower characteristics were affected significantly by temperature, except for flower position within the plant. Higher temperatures increased NFPP, mainly by increasing the number of flower buds, but decreased individual flower size. The temperature effect was also dependent on the phase of the cultivation period. In general, flower characteristics were less sensitive to temperature applied during the long-day period. NFPP was affected positively by temperature, mainly during phase III, whereas individual flower size increased with temperature during phase II, but decreased with temperature during phase III. Lower temperatures during phase III significantly enhanced flower colour intensity. Interest in using a more dynamic heating strategy is discussed.