Effects of genotype and environment on seed chlorophyll degradation during ripening in four cultivars of oilseed rape (Brassica napus)

Abstract

The rate of chlorophyll degradation in ripening canola seed was investigated using two sowing dates in each of 2 yr at one location and four cultivars of oilseed rape (Brassica napus), Westar, Regent, Global and Tribute. In general, the cultivars had the same rate of chlorophyll breakdown when grown in the same environment. All cultivars had a slower rate of chlorophyll breakdown in the late versus the early seeding date. The chlorophyll degradation rate using log ppm chlorophyll versus days showed significant differences between the two seeding dates and 2 yr in the study. The use of growing degree days (GDD) to determine rate of chlorophyll degradation removed many of these significant differences, confirming a major influence of temperature on the rate of chlorophyll breakdown. A second study correlating swathing date and chlorophyll levels in harvested canola seed indicated that rapid moisture loss from the seed fixed the chlorophyll at a higher level than that obtained with a slow moisture loss. Seeds harvested from the side branches contained more chlorophyll than seeds from the main stems. Late seeding resulted in higher seed chlorophyll levels at harvest. Low seed chlorophyll levels could be achieved if canola was sown early, using a high seeding rate to reduce branching, and swathed at physiological maturity under conditions which allow for slow moisture loss from the seed in the field.Key words: Oilseed rape, seed chlorophyll, Brassica napus