Abstract
Seedlings of Primula malacoides Franch `Prima Carmine Red' and Primula vulgaris Huds.`Danova Lemon Yellow' received supplemental irradiance from high pressure sodium lamps for 2 weeks initiated at germination, 14 days after germination or 28 days after germination. The plants were grown at 15 ± 3C, 16 hours photoperiod and except during treatment, an average photosynthetic photon flux of 100 μmol·s-1m-2 (5.8 mol· day-1m-2). The irradiance levels during treatment were 200 or 300 μmol·s-1m-2 (11.5 or 17.3 mol·day-1m-2). There were no significant effects of supplemental irradiance on rate of flowering for P. malacoides, although the leaf number on the main shoot increased from 22 ± 4 leaves for control plants to 30 ± 3 leaves for plants receiving 300 μmol· s-1m-2. Flowering of P. malacoides averaged 100 ± 4 days from germination. Two weeks of 300 μmol· s-1m-2 initiated 4 weeks after germination resulted in an average plant dry weight of 0.56 ± 0.07 g compared to an average 0.39 ± 0.05 g for plants continuously grown at 100 μmol· s-1m-2.
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