ISHS Acta Horticulturae 580: IV International ISHS Symposium on Artificial Lighting
POSSIBILITIES FOR USING PHOTOPERIODISM TO PROGRAM FLOWERING OF SUNFLOWERS (HELIANTHUS ANNUUS) IN THE GREENHOUSE AND IN THE OPEN |
| Authors: | T. Blacquière, N. Straver, D. van den Berg |
| Keywords: | Helianthus annuus ¿Sunrich Orange¿ and ¿Sunbright¿, critical daylength, cut flower, juvenility |
| Abstract:
The aim of this study was to investigate the response of sunflowers to long and short days, both in the seedling stage and later, during cultivation of the adult plants. A second series of experiments dealt with the critical daylength: what has to be considered a long and a short day for sunflowers. In a third series of experiments we tried to pre-cultivate and program the seedlings during their stay in plant trays in such a way that they would flower early after planting in the open air, despite the long-day conditions. In the first weeks after sowing, we found that sunflowers respond to short days with flower induction. Long days postponed flowering. Continuous application of short days resulted in flowering plants of 50 cm length, whereas continuous long days resulted in 3 m length plants. A marketable length should be somewhere in between. Comparing photoperiods of 10, 12, 14 and 16 hours (and later 11, 12, 13, 14 hours) led to the conclusion that the window is rather narrow: every daylength smaller than 12 hours is a short day, and all daylengths over 14 hours are long days. This was true for young seedlings (before three to four weeks from sowing) and for adult plants. The response to photoperiod during the three week seedling stage, was used to program plants by lighting and darkening before planting in the field. | |
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