Effects of photoperiod, temperature and bud size on ¯owering in Metrosideros excelsa (Myrtaceae)

Abstract

SummaryThe effects of photoperiod, temperature and bud size on ¯oral initiation and development were examined in two cultivars (Scarlet Pimpernel and Vibrance) of Metrosideros excelsa (family Myrtaceae). Two complementary experiments were conducted. In the ®rst, a factorial combination of two photoperiods (10 or 16 h) and two temperature regimes (12/98C or 17/148C) was applied for 0, 5, 10 or 15 weeks before plants were transferred to a forcing greenhouse at 24/178C. Plants transferred from the 17/148C and 10 h photoperiod treatment after 15 weeks had the highest proportion of ¯owering plants, with signi®cantly more in¯orescences per plant. In general, no ¯owering was observed in plants transferred after 0, 5 or 10 weeks. In a second experiment, carried out simultaneously with the ®rst, the same cultivars were grown continuously in four greenhouses using a factorial combination of two photoperiod treatments (ambient daylength or 16 h) and two temperature treatments (ambient temperature or 24/178C) until plants reached anthesis. The ambient daylength/ambient temperature conditions produced a higher proportion of ¯owering plants, and a signi®cantly greater number of in¯orescences per plant. No ¯owering occurred under the 24/178C and 16 h regime. In both experiments, buds initially 2.0±3.0 mm in diameter had the highest probability of becoming ¯oral; buds less than 2.0 mm in diameter were more likely to remain vegetative or unbroken. Rates of ¯oral development varied signi®cantly between treatments.