EFFECTS OF TEMPERATURE ON THE FLOWER SIZE OF PANSY (VIOLA X WITTROCKINNA GAMS)

The effects of temperature on the flower size of pansy were investigated in two experiments under both glasshouse and controlled environment conditions. Under glasshouse conditions, flower size (mm(2)) decreased linearly with increasing temperature between 9 and 31 degrees C (r(2) = 0.72). A transfer experiment showed that the decrease in flower size was proportional to the magnitude of the increase in temperature and to the duration of exposure. Thus, prolonged exposures to higher temperatures led to progressively smaller flowers. Temperature prior to visible bud stage had little effect on final flower size, but all subsequent stages were equally sensitive to increased temperatures. Thus, a period of high temperature had the same affect regardless of the stage of floral development. A proportion of the reduction in final flower size to temperature could be attributed to changes in the duration of flower development with temperature. A model was developed which showed that final flower size could be accurately predicted assuming that it was a simple function of mean temperature during flower development and that temperature affected flower size equally throughout development. Fastest rate of flower development from visible bud was found at a temperature of 25 degrees C.