Temperature control of dormancy and germination in embryos isolated from seeds of dormant and nondormant lines of wild oats (Avena fatua)

The question of whether the embryo is the site of the observed effect of low and high temperatures during seed maturation on the final dormancy of ripe seeds of wild oats (Avena fatua L.) was investigated. Embryos isolated from seeds of dormant lines germinated within 2–3 weeks of incubation at an optimum temperature (4 °C), irrespective of maturation temperature. However, whole seeds were dormant for several months except for the temperature-sensitive line, AN 86, where relatively high maturation temperatures significantly reduced the period of primary dormancy. There was no difference between the germinative capabilities of embryos isolated from the temperature sensitive AN 86 and the relatively less sensitive line AN 51. Thus, the mechanisms underlying the dormancy of whole seeds, as well as the temperature effects on dormancy, do not appear to reside within the embryo. Further experiments were conducted to resolve the apparent discrepancy between earlier conclusions that embryos of dormant wild oats are dormant and the present findings that they are not. The earlier hypothesis was based on lack of germination in embryos of a nonlocal line, Montana 72, incubated at 20 °C. In the present study, embryos of Montana 72 were not dormant when incubated at 4–12 °C, but were induced to thermodormancy when incubated in temperatures above that range. Embryos of local lines (AN 265, AN 51, and AN 86) germinated readily at all temperatures below 24 °C, but showed thermodormancy above it. Thus, isolated embryos of dormant lines are capable of germination at optimum temperatures, but are thermodormant at relatively high temperatures.