Environmental × Genotype Effects on Seed Dormancy and After‐Ripening in Wheat 1

The length of the after‐ripening period (ARP) for winter wheat ( Triticum aestivum L.) in the Pacific Northwest of the United States is very important. If the ARP is too long, fall planted seeds will not germinate uniformly, resulting in poor stands; preharvest sprouting may occur if the ARP is too short. The objective of this study was to examine the influence of cultivar and temperature during grain fill on the level of seed dormancy during ARP. Three winter wheat cultivars differing in susceptibility to preharvest sprouting were grown in five environments with varying rainfall and temperature conditions during grain fill. Grains were harvested at harvest ripeness and stored at −10, 10, 20, and 30°C during an 8‐week ARP. The level of seed dormancy was calculated using germination index and percent germination values determined at harvest ripeness and after an 8‐week ARP. Seed dormancy at harvest ripeness was a function of cultivar and environment during grain development. Loss of seed dormancy during after‐ripening was a function of the cultivar, the environment in which the grain developed, and the after‐ripening environment. Grains that developed in cool environments generally lost their dormancy more rapidly than grains that developed in warm environments. High temperatures during the ARP generally accelerated the loss of seed dormancy. One of the cultivars with low dormancy at harvest ripeness expressed higher levels of seed dormancy when stored at –10°C for 8 weeks than when it developed under certain field conditions. Environmental conditions typical of the Pacific Northwest, cool temperatures during grain development followed by high temperatures after harvest ripeness of the seed, are conducive to rapid loss of seed dormancy, which may lead to severe preharvest sprouting if grain harvest is delayed.