Poinsettia Developmental and Postproduction Responses to Growth Retardants and Irradiance

Abstract

Plants of Euphorbia pulcherrima Wind. `Glory' were grown under total irradiances of 13.4, 8.5, or 4.0 mol·m-2·day-1 and sprayed with water (control), 2500 mg daminozide/liter + 1500 mg chlormequat chloride/liter (D + C), 62.5 mg paclobutrazol/liter, or 4, 8, 12, or 16 mg uniconazole/liter to ascertain plant developmental and postproduction responses to treatment combinations. Anthesis was delayed for plants grown under the lowest irradiance. Anthesis was delayed by the D + C treatment, whereas other growth retardant treatments had no effect on anthesis date. Irradiance did not affect plant height at anthesis, but all growth retardant treatments decreased height over control plants. Inflorescence and bract canopy diameters were decreased at the lowest irradiance level. Growth retardants did not affect individual inflorescence diameters, but all, except paclobutrazol and 4 and 8 mg uniconazole/liter, reduced bract canopy diameter compared with control plants. Plants grown under the lowest irradiance developed fewer inflorescences per plant and fewer cyathia per inflorescence. Cyathia abscission during a 30-day postanthesis evaluation increased as irradiance was decreased; cyathia abscission was unaffected by growth retardant treatment. Leaf abscission after 30 days postanthesis was lowest for plants grown under the lowest irradiance. At 30 days postanthesis, all growth retardant treatments increased leaf abscission over controls. Results indicate that irradiance and growth retardant treatments during production can affect poinsettia crop timing, plant quality at maturity, and subsequent postproduction performance. Chemical names used: 2-chloroethyl-N,N,N-trimethylammonium chloride (chlormequat chloride); butanedioic acid mono (2,2-dimethyl hydrazide) (daminozide); β-[(4-chlorophenyl) methyl]- α -(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol), (E)-1-(p-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-l-penten-3-ol (uniconazole, XE-1019).