Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/20/2004
Publication Date: 11/1/2004
Citation: Kasperbauer, M.J., Loughrin, J.H. 2004. Butterbean seed yield and protein content are affected by photomorphogenesis. Crop Science. 44:2123-2126. Interpretive Summary: Butterbean is a popular Southern food crop that is consumed as fresh unripe seed or after storage as ripe seed. In either case, yield and nutrient content are important. This crop is often grown in drip-irrigated, raised-bed rows that are covered with black plastic mulch to conserve water and control weeds. Scientists at the Coastal Plains Soil, Water and Plant Research Center in Florence, SC, hypothesized that growing the plants over colors of plastic other than standard black could affect seed yield and seed protein content of ripe beans. Speckled areas on the surface of ripe seed contain anthocyanins that serve as antioxidants. Black, red, green, yellow, and white surface colors reflected different quantities and ratios of far-red, red, and blue light to the plants from germination through bean ripening. The colors of light were chosen to act through the plants' natural growth regulating system to influence allocation and use of compounds generated by photosynthesis. Highest seed yields occurred with a red mulch that reflected very little blue and a high ratio of far-red to red light. Lowest seed yields occurred over green and standard black mulches. Bean speckling was most abundant over red and yellow mulches, and lowest over green, suggesting an influence on antioxidant content of this food crop. Highest protein yield per plant was found over red mulch. It was concluded that color of reflected light received during plant development can influence the yield and nutrient content of speckled butterbeans.
Technical Abstract: Yield and seed protein content of edible beans are important to growers and consumers. We hypothesized that some colors of light reflected to growing bean plants could affect photomorphogenesis enough to result in greater seed yield and protein content. Speckled butterbean (Phaseolus lunatus L.) was used as the test crop because it is a popular food crop, and the speckled areas contain anthocyanins which function as antioxidants. The plants were grown in drip-irrigated, raised-bed rows that were covered with plastic mulch to conserve water and to reflect morphogenic light. Black, red, green, yellow, and white mulch surface colors were used to reflect different quantities and ratios of far-red (FR), red (R), and blue (BL) light to the plants from emergence to ripening of seed. The highest seed yield occurred over a red mulch that reflected very little BL, a high R/BL ratio, and a FR/R ratio higher than the ratio in incoming sunlight. Lowest yields occurred over green and standard black mulches. The area of seed coat covered by anthocyanin-containing dark speckles was highest over red and yellow mulches, and lowest over green, suggesting a possible influence on antioxidant content in this food crop. Significantly higher amounts of seed protein per plant were found in beans that developed over the red mulch. We conclude that color of light reflected to developing butterbean plants can act through the natural regulatory system within the growing plants to alter physiological processes enough to result in greater seed yield and greater amount of seed protein per plant.