POINSETTIA DEVELOPMENTAL AND POST-PRODUCTION RESPONSES TO GROWTH RETARDANTS AND IRRADIANCE

Abstract

Plants of Euphorbia pulcherrima Wind. `Glory' were grown under 13.4, 8.5, or 4.0 mol·m-2·day-1 and sprayed with water (control); 2500 mg·liter-1 daminozide + 1500 mg·liter-1 chlormequat chloride (D+C); 62.5 mg·liter-1 paclobutrazol; or 4, 8, 12 or 16 mg·liter-1 uniconazole to ascertain plant developmental and pest-production responses to the treatment combinations. Days to anthesis increased as irradiance was decreased. Anthesis was delayed by the D+C treatment, while other growth retardant (GR) treatments had no effect on anthesis. Irradiance did not affect plant height at anthesis, but all GR treatments decreased height over control plants. Bract display and bract canopy display diameters declined as irradiance was decreased. Growth retardants did not affect individual bract display diameters, but all GR treatments except paclobutrazol reduced bract canopy display diameter. Plants grown under lower irradiance had fewer axillary buds develop, fewer bract displays per plant, and fewer cyathia per bract display. Cyathia abscission during a 30 day post-anthesis evaluation was not affected by treatment; however, plant leaf drop was linearly proportional to irradiance. All GR treatments increased leaf drop over controls, and the D+C treated plants had the highest leaf loss. Results indicate the irradiance and GR treatments during production can affect poinsettia crop timing, plant quality at maturity, and subsequent post-production performance.