Maternal Temperature Imposes a Longer-Term Effect on Seedling Emergence Than Does Genetic Variation in Seed Dormancy

Germination represents the first major transition in plants, and seed dormancy influences germination timing. However, the mechanism by which variations in seed dormancy due to genetic variation or the maternal environment influence germination timing has not been studied in depth. In this study, the effects of temperature during seed maturation (maternal temperature) and genetic variation on weedy rice seedling emergence in a field environment were evaluated. The experiments were repeated for 4 years using seeds collected from weedy rice groups, which represented different degrees of seed dormancy. The maternal temperature was evaluated via the yearly variation in the field temperature. Genetic variation had a greater effect on seedling emergence during unfavourable seasons than during favourable seasons. A higher maternal temperature delayed seedling emergence during favourable seasons. The notable impact of global warming on seedling emergence has been confirmed over the past 15 years, and this impact will continue even under the sustainable CO₂ emission scenario. Maternal effects have long-term effects on seedling emergence at relatively high maternal temperatures, and these effects may increase under global warming.