Effect of Light Quality and Intensity on Flower-Bud Formation and Plant Height in Water Spinach (Ipomoea aquatica Forsk.)

Abstract

Artificial light conditions were changed to elucidate flower-bud formation and shoot elongation in water spinach. A local variety from Taiwan was used for the indoor experiments. Clones were propagated and cultivated under a 200 μmol m^-2 s^-1 of photosynthetic photon flux density (PPFD) controlled by using fluorescent lamps. The experiments were performed over a period of 30 days under artificial light conditions with variety in the light spectrum, irradiation duration and irradiance level. The effects of the light spectrum and irradiation duration on flower-bud formation and plant height were investigated using different LED sources (Exp. 1). The experimental plots were exposed to light from blue (B), green (G), or red (R) LEDs, and the irradiation duration was set at 10, 12, and 14 h at 200 μmol m^-2 s^-1 of PPFD in each plot. Irradiance levels of plot B were set at 50,100,150, and 200 μmol m^-2 s^-1 of PPFD to evaluate the effects of B-light irradiance on flower-bud formation (Exp. 2). The irradiation duration was set at 10 and 12 h for each irradiance level. Regardless of irradiation hours, plants were significantly higher in the B plot than in the G and R plots. Flower buds were observed in the B plots with 10 and 12 h irradiation, unlike in the G and R plots and in the B plot with 14 h. Under B irradiation, flower buds were observed with 100, 150, and 200 μmol m^-2 s^-1 of PPFD for 10 h, and 200 μmol m^-2 s^-1 of PPFD for 12 h. Increase of the irradiance level of B, shortened the days to flower-bud formation, and increased the number of flower buds.