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Meriam G. Karlsson and Jeffrey W. Werner

The potential photoperiodic effects and interactions with temperature were identified for flowering of german primrose (Primula obconica). The german primrose `Libre Light Salmon' was grown at long days (LD, 16 hours) or short days (SD, 8 hours) and 61 or 68 °F (16 or 20 °C). Visible bud (VB, 2-mm flower buds) averaged 90 days from seeding for plants grown at 61 °F independent of photoperiod or at 68 °F under LD. At 68 °F and SD, VB was delayed and flowering (horizontal petals) had not been observed at termination of the study (146 days from seeding). Flowering averaged 111 days at LD and 68 °F, 122 days at LD and 61 °F, and 133 days at SD and 61 °F. When plants within each temperature were shifted at weekly intervals from one photoperiod to the other, increasing duration of initial SD resulted in slower VB and at 68 °F more than 8 weeks resulted in no flowering. Changing to SD from initial LD did not affect VB or flowering at either 61 °F or 68°F. These results suggest flowering of german primrose is faster under LD than SD at the recommended production temperatures of 65 to 68 °F (18 to 20 °C).

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Meriam G. Karlsson and Jeffrey W. Werner

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.

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Meriam G. Karlsson and Jeffrey W. Werner

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.

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Meriam G. Karlsson and Jeffrey W. Werner

Plants of Begonia ×tuberhybrida Voss. `Nonstop', `Clips', and `Musical' were exposed to 0, 1, 2, 3, or 4 weeks of short days (SD, 9-hour daylength) initiated at 0, 4, or 8 weeks following germination. Plants grown under long days (LD, 16-hour daylength) flowered 68 (`Musical'), 78 (`Clips'), or 83 days (`Nonstop') after germination. Exposure to SD delayed flowering in all three cultivars. The delay in `Nonstop' and `Clips' was independent of plant age at time of SD exposure. One to 4 weeks of SD delayed flowering 11 to 14 days in `Nonstop'. In `Clips', the delay in flowering increased linearly from 7 to 19 days with increasing duration of SD. Flowering was delayed up to 15 days in `Musical' when SD were begun 0 or 4 weeks after germination. Exposure to SD during the final 4 weeks of development did not affect flowering in `Musical'. Exposure to SD did not affect shoot, leaf, or flower number in any of the cultivars. The root/shoot dry-weight ratio within cultivars was independent of daylength.