Spectral Sensitivity of the Extension Growth of Tulips Grown with Night Lighting under a Natural Photoperiod

Abstract

The effect of light quality on the extension growth of tulips was investigated for 4 tulip (Tulipa gesneriana) cultivars "Leen van der mark," "Murasaki suisho," "Come back," and "Kikomachi." The exposure of tulips to ultraviolet-A (UV-A), blue (B), red (R) or far-red (FR) fluorescent tubes throughout the entire night (a process called "night lighting") was found to promote lengthening of the stem and first internode of plants grown under natural photoperiod conditions in a greenhouse. The effectiveness of FR night lighting was consistently observed across 4 cultivars, although the effectiveness of illumination within the UV-A, B and R wavelength ranges was found to vary with respect to stem length, the first internode and among different cultivars. Elevated photon flux densities of FR light were found to quantitatively increase the extension growth of "Leen van der mark," but the effect of FR night lighting reached saturation point at 0.59 mol m-2 s-1. A 4-h end-of-day lighting period and night-break FR lighting period were also found to promote extension growth, but these effects were less pronounced than that induced by FR night lighting. A 4-h end-of-night FR lighting period had no effect on extension growth. Apart from these findings, the effects of the light quality on extension growth are discussed.