Chlorophyll degradation in summer oilseed rape and summer turnip rape during seed ripening

Chlorophyll breakdown in ripening seed of three summer rape cultivars (Brossica napus L.) and one summer turnip rape cultivar (Brassica rapa L.) was investigated to clarify the influence of genotype, environment, seed moisture and endogenous ethylene production. Final seed chlorophyll levels were determined for summer oilseed rape and turnip rape cultivars grown at several locations during 4 yr. Both genotype and environment affected seed chlorophyll levels at harvest, but genotype by environment interactions were minimal for the cultivars included in this study. Differences in maturity did not adequately explain the genotypic variation among the rape cultivars tested. Rates of seed chlorophyll breakdown, moisture loss and ethylene evolution were measured in ripening seeds of three rape cultivars. Stellar, Delta and Westar had significantly different rates of seed chlorophyll breakdown. Lower temperatures resulted in slower chlorophyll degradation. Chlorophyll and moisture (expressed as percentage seed mass) were positively correlated in ripening seed, but moisture loss occurred at the same rate during seed ripening in all cultivars and environments. Chlorophyll and endogenous ethylene production were positively correlated, but the peak of ethylene production occurred after moisture loss and chlorophyll breakdown had begun, implying that an increase in endogenous ethylene was not the trigger for the initiation of these events. Key words: Chlorophyll degradation, green seed, ripening, moisture loss, ethylene, oilseed rape, turnip rape