TEMPERATURE REGIMES TO CONTROL PLANT STATURE: CURRENT UK R&D
Controlled environment cabinet experiments showed that shoot length in poinsettia (Euphorbia pulcherrima) was reduced when the temperature during the whole of a 12h day was held at 4°C below that of the night (-4°C DIF). However, increasing the differential to 12°C (-12°C DIF) was less effective in reducing shoot length. Negative DIF responses resulting in a decreased shoot length appeared to be largely due to the plant's low-temperature sensitivity during the first 3h of the day. The efficacy for height control in poinsettia of a brief duration temperature drop starting at sunrise was confirmed in a subsequent glasshouse experiment. Parallel cabinet experiments with geranium (Pelargonium x hortorum) showed this species to be less responsive to DIF treatments than poinsettia. However, reductions in both stem and petiole lengths were given in extreme cases. A 6°C drop for 2h starting at dawn in a subsequent glasshouse experiment gave negligible reductions in height. Greater reductions were given in Salvia splendens, Impatiens walleriana and Petunia x hybrida. A pre-sunrise temperature drop was much less effective with these bedding plant species. The use of negative DIF treatments caused a degree of leaf chlorosis, particularly in poinsettia, due to decreased chlorophyll content. This was especially marked in the -12°C DIF treatment. Negative DIF treatments which were effective in reducing stem length in poinsettia were associated with an advancement of flowering. This advancement was particularly pronounced when compensating higher temperatures were given during the remainder of the 24h period in order to maintain a given 24h average temperature.
Langton, F.A., Cockshull, K.E., Cave, C.R.J. and Hemming, E.J. (1992). TEMPERATURE REGIMES TO CONTROL PLANT STATURE: CURRENT UK R&D. Acta Hortic. 327, 49-60