THE EFFECT OF DAY AND NIGHT TEMPERATURE AND IRRADIANCE ON DEVELOPMENTOF CATHARANTHUS-ROSEUS (L) GRAPE COOLER

The effects of day and night temperatures (15 to 35C) and three irradi ance levels [50% of ambient, ambient, and ambient plus 12 mol . m(-2). day(-1) of supplemental photosynthetic photon flux (PPF)] on developm ent of Catharanthus roseus 'Grape Cooler' were determined, Time to flo wer decreased by 30 days and leaf-pair unfolding rate (LUR) increased linearly as average daily temperature increased from 18 to 35C. Flower size was greatest when plants were grown at 25C. Supplemental light d ecreased days to flower and increased flower size. Flowering occurred when nine leaf pairs were present on the plant. Using the inverse of t he LUR curve, i.e., days per leaf pair, the number of days to flower c ould be predicted at any time during plant development based on plant leaf number.