THE EFFECTS OF TEMPERATURE, PHOTOPERIOD AND LIGHT INTEGRAL ON THE TIME TO FLOWERING OF PANSY CV UNIVERSAL VIOLET (VIOLA X WITTROCKIANA GAMS)

The effects of temperature, photoperiod and light integral an the time to first flowering of pansy (Viola x wittrockiana Gams) were investig ated. Plants were grown at six temperatures (means between 14.8 and 26 .1 degrees C), combined with four photoperiods (8, 11, 14 and 17 h). T he rate of progress to flowering increased linearly with temperature ( up to an optimum of 21.7 degrees C) and with increase in photoperiod ( r(2) = 0.91, 19 d.f.), the latter indicating that pansies are quantita tive long day plants (LDPs). In a second experiment, plants were sown on five dates between July and December 1992 and grown in glasshouse c ompartments under natural day lengths at six temperatures (means betwe en 9.4 and 26.3 degrees C). The optimum temperature for time to flower ing decreased linearly (from 21.3 degrees C) with declining light inte gral from 3.4 MJ m(-2) d(-1) (total solar radiation). Data from both e xperiments were used to construct a photothermal model of flowering in pansy. This assumed that the rate of progress to flowering increased as an additive linear function of light integral, temperature and phot operiod. Independent data from plants sown on three dates, and grown a t five temperatures (means between 9.8 and 23.6 degrees C) were used t o validate this model which gave a good fit to the data (r(2) = 0.88, 15 d.f.) Possible confounding of the effects of photoperiod and light integral are discussed. (C) 1997 Annals of Botany Company.