Changes in embryo dormancy of capeweed [Arctotheca calendula (L.) Levyns.] seeds in response to temperature were investigated to determine the nature of seasonal dormancy cycles. Primary embryo dormancy persisted for 2–3 months after seed collection and was then rapidly relieved when seeds were maintained at temperatures simulating summer soil surface temperatures. Embryo dormancy was also rapidly relieved in seeds maintained at constant temperatures, indicating that a daily temperature fluctuation was not necessary for the relief of embryo dormancy in capeweed. Dormancy relief was maximal at 40°C. Secondary dormancy was induced when seeds were maintained at low temperatures and a water potential of –1.5 MPa, suggesting that the onset of winter may postpone germination until a subsequent autumn. These results indicate that the dormancy cycles observed in capeweed seeds maintained on the soil surface are probably driven by seasonal changes in soil temperature.
