Effect of environment and applied chemicals on the flowering and form of Geraldton Wax ( Chamelaucium uncinatum Schauer)

Abstract

Flowering in a number of cultivars of Geraldton Wax ( Chamelaucium uncinatum Schauer) is promoted by exposure to short days. For the cultivar ‘Purple Pride’ the critical photoperiod above which flowering does not occur was between 13 and 13.5 h for 3–4-month-old plants grown from cuttings. In 14 and 16 h photoperiods no flowering occurred in these young plants, although in plants older than 5 or 7 months there was often a low level of flowering. One cultivar failed to flower in any daylength and in a hybrid line there was a complex response to temperature and photoperiod. Temperatures of 20–25°C and high irradiance favoured flowering of ‘Purple Pride’. At lower temperature (below 16°C) there was poor flowering. The flowers also developed more slowly but were larger when open. Higher temperature (above 25°C) led to rapid flower bud appearance, but flower number was drastically reduced and the flowers were much smaller. Cool (12–15°C) temperatures imposed during 3–6 weeks of short days blocked the induction of flowering. By contrast, these temperatures were favourable for flowering of a hybrid between Chamelaucium floriferum and C. uncinatum, although the effect of daylength was far greater. Flower development proceeded even at these cool temperatures. Both paclobutrazol and chlormequat inhibited shoot growth and generally had little effect on flowering. Benzyladenine caused substantial branching and could either depress or promote flowering. Flower drop was triggered within 3 days with ethephon. The implications of these findings for the regulation of flowering under field and greenhouse conditions are discussed.