Effects of temperature during ripening period on seed coat color of azuki bean.

摘要

Seed coat colour and size are important characters of azuki bean (Vigna angularis). Two experiments were conducted to determine the effects of temperature (5, 15, 30 and 40 degrees C for 2, 4, 6, 8, 10, 12 and 14 days) during the ripening period on the seed coat colour of azuki bean cv. Erimoshouzu. Seed coat colour was expressed by an XYZ colour system. The effect of temperature on seed coat colour was apparent in immature pods but was small in fully ripened pods. As temperature rose, the dominant wavelength of hue increased, but the Y value decreased. Excitation purity of chroma in fully ripened pods decreased as temperature rose, but that in immature and partially ripened pods increased as the temperature rose up to 30 degrees C, then decreased at 40 degrees C. In a field experiment conducted in Japan, the mean temperature 10 days after the young pods became white in appearance had a high positive correlation with a dominant wavelength (r=0.913), and negative relationships with a Y value (r=-0.983) and excitation purity (r=-0.893). These results indicate that when the temperature during ripening period is high, seed coat colour becomes darker since the dominant wavelength becomes longer, and Y value and excitation purity become small. Estimation formulas for seed coat colour at harvest time were proposed. YD (dominant wave)=0.7947x + 591.3, YY (Y value)=-0.3452x + 12.64 and YE (excitation purity)=-0.5507x + 44.4, where x is the mean temperature (measured by using the average temperature of 30 years) for 10 days after the young pods became white in appearance.