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

The effects of photoperiod. temperature and bud size on floral initiation a nd development were examined in two cultivars (Scarlet Pimpernel and Vibran ce) of Metrosideros excelsa (family Myrtaceae). Two complementary experimen ts were conducted. In the first, a factorial combination of two photoperiod s (10 or 16 h) and two temperature regimes (12/9 degrees C or 17/14 degrees C) was applied for 0, 5, 10 or 15 weeks before plants were transferred to a forcing greenhouse at 24/17 degrees C. Plants transferred from the 17/14 degrees C and 10 h photoperiod treatment after 15 weeks had the highest pro portion of flowering plants, with significantly more inflorescences per pla nt. In general, no flowering was observed in plants transferred after 0, 5 or 10 weeks. In a second experiment, carried out simultaneously with the fi 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 24/17 degrees C) until plants reached anthesis. The ambient daylength/ambient temperature conditions produced a higher proportion of flowering plants, and a signifi cantly greater number of inflorescences per plant. No flowering occurred un der the 24/17 degrees C and 16 h regime. In both experiments, buds initiall y 2.0-3.0 mm in diameter had the highest probability of becoming floral; bu ds less than 2.0 mm in diameter were more likely to remain vegetative or un broken. Rates of floral development varied significantly between treatments .