|ANTONIOUS, G - KY STATE UNIV
|BYERS, M - KY STATE UNIV
Submitted to: Photochemistry and Photobiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/2/1996
Publication Date: N/A
Interpretive Summary: Mulches are often used in field production of vegetables to conserve water and control weeds with less applied herbicides. Color of light reflected from mulches can affect leaf size, root size, and the shoot/root weight ratio. We wondered whether flavor of edible roots might also be affected by color of light reflected from mulch to growing leaves. Turnip plants were grown with blue, green, and white mulches in trickle-irrigated field plots. The blue and green mulches reflected different amounts of blue light (B), and both reflected high far-red to red (FR/R) ratios. Plants grown with blue and green developed longer leaves and smaller roots than plants grown with white mulch (which reflected a lower FR/R ratio). Taste tests by people indicated that turnip roots grown with blue mulch had the sharpest flavor, and those grown with green were mildest. Roots grown with blue (versus green) mulch had higher concentrations of glucosinolates (compounds that give sharp flavor), and lower concentrations of soluble sugars. We conclude that the FR/R ratio reflected to the growing leaves dominated regulation of leaf and root size, and that the amount of blue light reflected to leaves affected the quantity of glucosinolates (or their precursors) that translocated to the roots. To the best of our awareness, this is the first documentation that light reflected from colored mulches to leaves of growing plants can affect flavor of edible roots.
Technical Abstract: Plastic mulches are widely used to conserve water and control weeds with less applied herbicides in production of high-value food crops. Effects of colored mulches on leaf and root size, and flavor of edible roots were studied in turnip (Brassica rapa L.) grown in trickle-irrigated field plots with blue, green, and white mulches. The blue and green mulches reflected different amounts of blue light (B), but they both reflected far-red to red (FR/R) ratios higher than the ratio in incoming sunlight. The white mulch reflected more photosynthetic light and a lower FR/R ratio than the blue or green mulches. Plants grown with blue and green mulches did not differ significantly in leaf length, root size, and shoot/root biomass ratio. Those grown with white had shorter leaves and larger roots. Plants grown with blue mulch developed roots with a sharp flavor, and roots grown with green mulch had a mild (almost sweet) flavor. Those grown with white had a less distinct flavor. Roots grown with blue (versus green) mulch had higher concentrations of total glucosinolates (GSL's) and lower concentrations of reducing sugars. The main difference in light reflected from blue versus green was the amount of reflected B, suggesting that B influenced an enzyme involved in the pathway from glucose to glucosinolate. We conclude that light reflected from colored mulch can influence not only shoot/root biomass ratio but also flavor-related chemical composition of field-grown food crop plants.