Changes in sensitivity of Amaranthus retrof/exus L. seeds to ethylene during preincubation. I. Constant temperatures

Germination responses of redroot pigweed (Amaranthus retroflexus L.) seeds to ethylene were determined at 25, 30, 35, or 40° C after preincubation at various temperatures (15–35° C) for different periods (0.5–32 d). After 7 d preincubation, seeds showed a log‐linear germination response to ethylene concentration in most of the temperature treatments. Sensitivity to ethylene increased with longer preincubation; response thresholds of 0.03−0.09 cm3 m−3 were observed after 32 d, compared to 0.18−1.6 cm3 m−3 after 7 d of preincubation. Preincubation at 15 or 20° C generally enhanced germinability, whereas 25 or 30° C produced secondary dormancy, which was readily broken with ethylene. Temperature during preincubation also significantly influenced the slope of the dose‐response curve. The responses of preincubated redroot pigweed seeds to ethylene suggested that, in the field, seeds would probably not lose their sensitivity to this gas during prolonged burial in soil.