The Effect of Photoperiod, Temperature and Photon Flux Density on Flowering in Pimelea ciliata

Abstract

A range of photoperiods were investigated to determine their effect on newer induction in Pimelea ciliata. Temperatures and photon flux densities were also investigated to determine their effect on modifying the response to photoperiod. Pimelea ciliata developed flowers on all plants after exposure to at least 4 weeks of an 8 h photo- and thermoperiod at a high photon flux density. As the time under the 8 h photo- and thermoperiod increased, the total number of flowers produced and the percentage of buds which were floral on each flowering plant increased. Plants gown under a 16 or 10 h photoperiod for up to 8 weeks did not produce any flowers. Under a 12 h photoperiod, only two plants out of 36 flowered, and they produced a low number of flowers. Under the conditions tested, temperature had no apparent effect on the number of plants which flowered or the number of flowers on each flowering plant. However, a vernalisation response may be increasing the rate of flowering. The flowering response was reduced when plants were grown under a low photon flux density. Few plants produced flowers, and the percentage of shoots that were floral was also reduced under low light.