Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2002
Publication Date: N/A
Interpretive Summary: Concentrations of nutrient and health-related compounds such as B-carotene and ascorbic acid in food crop plants are influenced by a range of growth conditions, including light. It was hypothesized that concentrations of these compounds in edible roots could be modified by the amounts and ratios of blue, red and far-red light reflected from the soil surface to the growing leaves during enlargement of the edible roots. To test the theory spaced carrot plants were grown in trickle-irrigated field plots that were covered with different colored panels to reflect a range of blue, red and far-red to the leaves of the developing plants. Those grown over red panels developed the largest shoots, but smaller roots and the lowest root to shoot weight ratio. Roots from plants grown with a shade of yellow that reflected low blue coupled with high amounts of red, far-red and photosynthetic light developed roots with higher concentrations of B-carotene, ascorbic acid and soluble phenolics. More work is in progress on other nutrient and/or health related compounds in other kinds of edible plants. This information on photobilogical action of reflected light has potential to become a component in field production systems to improve quality control of plant products grown as phytonutraceuticals.
Technical Abstract: Improved yield and nutrient content of food crops are important to both growers and consumers. We hypothesized that color of light reflected from the soil surface to developing leaves of field grown plants could result in modified root yield and concentrations of B-carotene, ascorbic acid and phenolic compounds in edible roots. Carrot (Daucus carota L.) was used as the test plant. The plants were grown in trickle-irrigated field plots that were covered with panels that reflected various combinations of far-red (FR), red (R) and blue light (BL) to the growing leaves. The highest FR to R photon ratio reflected to developing leaves resulted in greatest shoot weight and the lowest root to shoot weight ratio. However, an increased quantity of photosynthetic light resulted in greater total weight per plant. Roots from yellow- and white- covered plots had highest concentrations of B-carotene and ascorbic acid. Those from yellow- and black- covered plots had highest concentration of phenolics. In general, concentrations were higher in cortex than in xylem tissues. We conclude that color of light reflected from the soil surface to developing carrot leaves can influence yield and chemical composition of edible roots. This discovery suggests that color of light reflected to growing shoots may also influence chemical composition of plant species used as phytonutraceuticals.