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.
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