568 Effect of Twilight and Temperature Difference (DIF) or Temperature Pulse at End-of-day on Height of Easter Lilies

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  • 1 Dept. of Plant Agriculture, Hort. Research Inst. of Ontario, Univ. of Guelph, Vineland Station, Ont., Canada, L0R 2E0

Potted bulbs of Lilium longiflorum Thunb. `Ace', `Nellie White', and `Snow White' were grown under either ambient photo period (APP), 8-h photo period using blackout (no twilight) between 1600 and 0800 HR (8PP) or 8PP extended with 1-h of low-intensity far-red radiation (9PP) at end-of-light period in a greenhouse with either a +5 °C DIF or a –5 °C DIF (= day – night temperature). In a second experiment, Easter lilies were also grown under APP, 8PP, and 9PP regimes with a constant day/night temperature (0 °C DIF) but with either a +5 °C or –5 °C temperature pulse for 3-h during end-of-light period. Each experiment was replicated twice and data was averaged over 2 years. The +5 °C DIF regime produced plants which were 19% taller than under –5 °C DIF. Plants grown under APP were 32% and 25% taller than under 8PP in the +5 °C and –5 °C DIF regimes, respectively. Regardless of the DIF regime, plant height under the 9PP was the same. In the second experiment, there was no significant difference in plant height of plants grown with the –5 °C compared with the +5 °C pulse at end-of-light period.

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