The effect of genotype, environment and agronomic practices on the chlorophyll level in harvested canola seed

Abstract

High levels of chlorophyll in harvested canola seed cause an increase in processing costs, lower returns for producers and poorer quality end products. The effects of genotype, environment and agronomic practices on seed chlorophyll levels were investigated in this study. When canola seed was frozen for up to one month, either in the pods or after removal, no significant reduction in chlorophyll was observed. Results from a swathing study indicate that seeds from the side branches contained 1.5 to 2 times as much chlorophyll as seeds from the main stems. Seed that was dried rapidly contained 1.5 to 6 times as much chlorophyll as seed allowed to mature in swaths in the field. When seeds from each treatment in the swathing study were subdivided according to size, the smallest seeds were found to contain the most chlorophyll. Seed from the treatments with the highest chlorophyll levels also contained the greatest amount of small seed. Chlorophyll degradation rates were investigated in four cultivars of Brassica napus as the seed ripened. No significant differences in the rate of chlorophyll breakdown were found between the different cultivars tested. Cultivars that require longer growing seasons to reach maturity were found to initiate seed chlorophyll degradation later in the growing season, increasing the chances that high levels will remain when the seed is harvested. The environment did affect the rate of chlorophyll degradation, as slower breakdown rates did occur in later sown plots. This was assumed to be due to the lower daily mean temperatures which occured later in the growing season. A number of cultivars of both B. napus and B. campestris grown at sites throughout Manitoba were measured for seed chlorophyll levels at harvest. No significant differences were found among different cultivars of B. campestris but the final chlorophyll levels of B. napus seed were extremely variable, both among triazine tolerant cultivars and those without triazine resistance. The environment also affected the seed chlorophyll level and there was a significant genotype by environment interaction. Seed samples of a number of cultivars taken from high chlorophyll sites were subdivided according to size and the smallest seeds were found to contain the most chlorophyll. The relationship between the percentage of small seed in any sample and the chlorophyll level was less defined in the "Agroman" material than in the swathing study.