PHOTOPERIODIC CONTROL OF DEVELOPMENTAL GROWTH IN BEGONIA × TUBERHYBRIDA

Abstract

Plants of Begonia x tuberhybrida `NonStop Orange', `Clips Orange' and `Musical Orange' were exposed to 1, 2, 3 or 4 weeks of short days initiated at 4 stages of plant development (immediately upon germination, 5 weeks after germination, 10 weeks after germination and 15 weeks after germination). Prior to and succeeding short days, plants were exposed to a day length of 16 hours at 100 μmol·m-2s-1. Short days were 9 hours at an irradiance level of 180 μmol·m-2s-1 to give the same total daily irradiance (5.8 mol· m-2day-1) as long day conditions. The temperature was maintained at 21° ± 4°C during the day and 18° ± 2°C during night. The observed growth and development responses were similar among the studied cultivars. During the period of 4 to 8 weeks after germination, the seedling height increased at an average rate of 0.7 mm day-1 for plants grown under long days and 0.3 mm day-1 for short day plants. The photoperiodic conditions did not affect the number of emerging leaves. The root development was more proliferate on plants allowed to develop under long days compared to plants exposed to short days during early development.