THE EFFECT OF LOW LIGHT INTENSITY ON FLORAL EVOCATION AND PLANT ARCHITECTURE IN PTILOTUS NOBILIS

Ptilotus nobilis has a prolific flowering habit and shows an early transition from vegetative to reproductive growth. This is the main barrier for successful propagation by cuttings. Experiments investigated the effect of low light intensity on floral induction and initiation in seed grown plants. Further data describing plant architecture and development was collected. Plants were grown under high (909.3 µmol m^-2 s^-1), medium (398.6 µmol m^-2 s^-1) and low light (229.3 µmol m^-2 s^-1) and cardinal events including axillary stem growth, visible bud stage, first floret opening, and spike maturity (when 2/3 of the florets are open) were identified. At maturity, height of main stem and axillary stems, inflorescence length, number of axillary stems and final leaf number were recorded. Leaf number increased under low light (20.9 leaves) compared to high light (17.9) and cardinal events were delayed. Under lowest light intensity, axillary stem growth and visible bud stage were delayed by 19.5 and 22.5 days respectively, first floret opening by 31.6 days and spike maturity by 29.8 days when compared to plants grown under high light. At maturity, plants under high light were shortest with 48.8 cm when compared to medium (64.2 cm) and low light (65.9 cm). Observations indicated that plants can be classified into short and tall genotypes regardless of the environment. Genotype and environment influenced stem height at maturity, but not the length of the inflorescence. Inflorescence length increased with higher light intensities (12.2 cm / high light, 8.6 cm medium light, 5.6 cm / low light). The main conclusion of this experiment was that shading delays development, but does not fully prevent flower evocation, but the increase of final leaf number indicates that the vegetative phase is prolonged.