Butterbean Seed Yield, Color, and Protein Content Are Affected by Photomorphogenesis

Yield and nutrient content of edible beans are important to growers and consumers. Our objective was to determine whether some colors of light reflected to growing bean plants could affect photomorphogenesis enough to result in greater seed yield. 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 rows that were covered with plastic mulch to conserve water and to reflect morphogenic light. Black served as the control; and red, green, and white mulch surface colors were used to reflect different quantities of blue (BL), red (R), and far-red (FR) light to the plants from emergence to ripening of seed. Seed yield over red was significantly greater than over black, green, or white. The area of seed coat covered by dark speckles was highest over red and lowest over black and green. Protein concentration on a seed weight basis did not differ among colors, but significantly more seed protein per plant was found in beans that developed over red than over black, green, or white surfaces. We conclude that altering the amounts of BL, R, and FR reflected to developing speckled butterbean plants can alter physiological processes enough to affect seed yield, anthocyanin-containing area on seed coats, and amount of seed protein per plant.