QUANTIFYING LEAF UNFOLDING IN THE POINSETTIA.

The rate of lateral shoot leaf unfolding was determined for poinsettia plants grown with day and night temperature (DT and NT) combinations ranging from 16 to 30°C in 1986 and 15 to 24°C in 1987. Leaf development was described with two functions; 1) The time (in days) from pinching to the appearance of the first three leaves (LAG); and 2) The leaf unfolding rate of subsequent leaves (LUR). LAG and LUR were temperature dependent with optima at about 26°C. A function with average daily temperature (ADT), day temperature (DT²) and night temperature (NT²) provided the best least squares model for both LAG and LUR. The ratio of DT² to NT² coefficients was the same as the ratio of day to night length suggesting that the effects of day temperature and night temperature on LAG and LUR were equivalent.
An hourly rate function was estimated as follows: LUR per hr (hLUR) =(-0.01447 + 0.001917 * T – 0.00003904 *T². Summing the hourly rates allows estimation of a daily leaf unfolding rate in a greenhouse with fluctuating temperatures.

Symposium on Bedding and Pot Plant Culture

Robert D. Berghage, Royal D. Heins, John E. Erwin

https://doi.org/10.17660/ActaHortic.1990.272.35