STEM ELONGATION OF CHRYSANTHEMUM IN RESPONSE TO END-OF-DAY LIGHT TREATMENTS AND PHOTOPERIOD

**STEM ELONGATION OF CHRYSANTHEMUM IN RESPONSE TO END-OF-DAY LIGHT TREATMENTS AND PHOTOPERIOD**

Authors:	J. Bjerregaard Lund, O. Körner, J. Mazanti Aaslyng, T.J. Blom
Keywords:	photomorphogenesis, light quality, far-red, red, Chrysanthemum morifolium, LEDs, daily light integral, twilight
Abstract: Controlling light quality at the end of day (EOD) by elimination of twilight can decrease elongation of some potted plants, but may depend on the duration of the photoperiod. This paper describes the effects of EOD supplemental lighting with different red/far-red ratios on plant development of potted chrysanthemums (Chrysanthemum morifolium Ramat. 'Coral Charm') grown under different photoperiods. The effects of three different EOD treatments were tested with red/far-red light ratios (R/FR; 600-700 nm/700-800 nm) of 0.4, 0.7 or 2.4. These three EOD lighting treatments were applied daily over a three week period for 30 min after three photoperiods (9, 14 and 19h) with an irradiance of 120 µmol m^-2 s^-1. Plants were taller when exposed to lower R/FR ratios. The relative effect of the EOD R/FR ratios on final stem length decreased with an increase in photoperiod, as the relative increases in height between the R/FR of 0.4 or 0.7 compared to 2.4 were 68 or 35%; 19 or 16%; or 16 or 14%, for the 9h, 14h or 19h photoperiod, respectively.
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