Polymorphism for vernalization requirement in a population of Avena fatua

Polymorphism for vernalization requirement has been observed within a population of wild oats, Avena fatua L., grown under greenhouse conditions. One group of plants was early flowering ("spring type," [Formula: see text]), whereas another was late flowering ("winter type," [Formula: see text]). Vernalization of the winter type was obtained by germinating seeds for 2 weeks at 4 °C and resulted in shortening the time to heading by 50 days. However, this polymorphism was not observed in the field when plants germinated before mid-May. Hence, vernalization requirements did not appear to have any adverse or beneficial effects on time to heading and may be a neutral character in this population. Nevertheless, the frequency of the winter type in the population increased significantly over 6 years. Mechanisms are suggested to account for this phenomenon.