To study the spectral light effects and enhance health promoting pigmentation in leafy vegetables or salads in a greenhouse in Tunja, Colombia, chard plants were exposed to sunlight filtered through polypropylene films of green, yellow, blue, red colour or transparent (control). Leaves of chard plants growing under coloured covers, developed a higher chlorophyll a/b ratio of 1.6-1.8:1 compared with those grown under transparent cover. The ratio of carotenoids/chlorophyll (a+b) was diminished 7.9-9.5% under yellow, green and blue covers compared to control, while red cover showed no difference with transparent cover. Accumulated dry mass was largest (4.8 g DM) under yellow film than in any other treatment (2.3-2.8 g DM). The present study found that the yellow cover induced better growth judged as dry matter, as compared to the control treatment as a consequence of the different contents on the amount of chlorophyll and carotenoids, as well as the higher photochemical quantum yield of PSII (F v /F m ). These results are discussed with relation to the intensity and spectral quality of light, and to the ratio of red/ far-red light (660/730 nm). Chard is used here as an example and the results may be transferable to other leafy vegetables or salads.
To determine the effects of light quality on the growth indices of plants, Pencas Blancas cultivar chard plantlets were grown for 2 months under five different light treatments, obtained by filtering sunlight through colored polyethylene films. The treatments included: red, blue, green, yellow and transparent cover colors. A transparent cover (white light) was used as the control. The colored covers affected the plant growth. The plants grown under the yellow cover presented a better behavior with regards to growth, taken as: total dry weight per plant, leaf area, specific leaf area, absolute growth rate, relative growth rate, harvestable dry matter and root to shoot ratio. The dry matter partitioning in the leaves and roots was affected by the light quality, but not in the petioles, with a higher accumulation of dry mass in the leaves of plants grown under the yellow cover. As a consequence of the enhanced leaf area in the plants under the yellow cover, they also had the highest water uptake. On the other hand, the highest net assimilation rate value was found in plants grown under the transparent cover. These results open up the possibility of using yellow colored cover in leafy green vegetables, especially in chard plants grown under controlled conditions.
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