Vernalization enforces seed dormancy in the agricultural weed Alopecurus myosuroides (Huds.)

Seed dormancy is the key factor determining weed emergence patterns in the field. Alopecurus myosuroides (black grass) is a serious cereal weed in Europe that experiences two emergence peaks affecting winter and spring cereals, respectively. Seedlings that emerge in autumn encounter a period of cold winter temperatures, whereas those that emerge in spring do not. In this work, we investigated the effects of this overwintering during vegetative growth on the primary seed dormancy of the offspring. Alopecurus myosuroides plants were propagated under controlled conditions where a proportion of the population was subjected to a simulated winter period (vernalization) as seedlings. The offspring produced by vernalized plants was significantly more dormant, requiring longer after-ripening and cold stratification treatments to germinate at warm temperatures. However, there was no difference in the range of temperatures under which dormant seeds germinated. We hypothesized that this difference in dormancy was the result of an epigenetic memory of vernalization. Global changes in DNA methylation of seeds were quantified using an ELISA-based approach. Imbibition in dormant seeds produced by vernalized plants was associated with a global demethylation event that was not observed in the offspring of plants that had not been vernalized. Taken together, these results demonstrate the importance of temperature at different stages of the plant lifecycle in determining dormancy levels and consequently weed emergence patterns in the field.