INFLUENCE D’UN PRE-TRAITEMENT AU FROID ET DE LA TEMPERATURE NOCTURNE SUR LA CROISSANCE, LE DEVELOPPEMENT ET LE CONTENU EN ELEMENTS MINERAUX DE PLANTS DE POINSETTIA

Abstract

To achieve more rapid adaptation of plants grown under a constant or split night temperature regime, two poinsettia cultivars (Euphorbia pulcherrima Willd ex. Klotzsch), Annette Hegg Dark Red (AHDR) and Annette Hegg Top White (AHTW), were given a cold pretreatment (PF). The PF was a 13 °C air temperature regime provided for 15 h a night during a 10-day period. The number of days to the first visible flower buds and to anthesis was longer for both cultivars having received a PF than the control plants (no pre-treatment). For AHDR only, plant height, top dry weight, the number and bract area were significantly lower after the PF when considering the average of the night temperature treatments. Regardless of the cultivar tested, no significant differences in bract diameter and root dry weight were observed between the control plants and those given a PF treatment. Whether the two cultivars were given a PF treatment or not, the split night temperature (TNP) of 16.3/14.2 °C caused a nonsignificant delay, from the appearance of first visible flower buds to anthesis, compared to those held at 16.7 °C. The most important delay of these parameters as well as the greatest reduction of bract area was obtained under a 10.8 °C night temperature. The TNP of 16.6/10.8 °C produced plants (PF or control), of both cultivars with a greater bract number and top dry weight. For the two cultivars given a PF treatment, the levels of nitrogen, phosphorus, calcium, and magnesium were greater when considering the means of the night temperature treatments.Key words: Euphorbia pulcherrima, cold pretreatment, night temperature, split night temperature