IRRADIANCE LEVEL AND DURATION REQUIRED TO TERMINATE THE DORMANCY OF BEGONIA X SEMPERFLORENS SEED

Begonia xsemperflorens-cultorum Hort. 'Prelude Scarlet' seeds varied w ithin irradiance treatments in the irradiance level and duration that they required to reach the light saturation value and germinate. At hi gh photosynthetically active radiation (PAR), seeds required light for only part of the germination period to terminate photodormancy, Germi nation >90% was achieved after 4 and 1 day of 24 hours/day exposure to PAR at 15 and 150 mu mol . m(-2). s(-1), respectively, but 82% germin ation occurred after 4 days of irradiance at 1.5 mu mol . m(-2). s(-1) at 27C. Fewer days to 50% of final germination (T-50) and between 10% and 90% germination (T-90 - T-10) were required when light saturation was achieved after 1 day at high PAR rather than after 4 days at a lo w PAR level. The total PAR that seeds received during 6, 12, or 24 hou rs of light daily determined the total percentage of the seeds that ge rminated. Seeds receiving 150 mu mol . m(-2). s(-1) continuously for g reater than or equal to 24 hours achieved 90% germination, but 6 or 12 hours daily at this irradiance level required 4 days and 3 days, resp ectively. Trends in total germination percentages (G), T-50, or T-90 - T-10 with increased PAR levels, hours of light daily, or days of ligh t were found by fitted regression equations and Tukey's HSD procedure. Begonia seed germination was promoted by PAR levels of 1.5 to 150 mu mol . m(-2). s(-1) for periods less than or equal to 4 days, with dark ness thereafter until cotyledon emergence.