Induction of Secondary Dormancy in Amaranthus hybridus Seeds by Summer Temperatures and Its Impact on Field Emergence

Abstract

In Amaranthus hybridus (smooth pigweed), the timing and magnitude of seedling emergence depend on seed dormancy. While winter temperatures are known to reduce dormancy in buried seeds, little is known about how summer conditions affect dormancy dynamics. This study aimed: (i) to quantify the changes that occur in the germination capacity of buried A. hybridus seeds during summer, (ii) to determine whether these seeds are induced into secondary dormancy by high summer temperatures and (iii) to establish whether the emergence pattern of this species is interrupted in autumn due to the re-imposition of dormancy during summer. In a laboratory experiment, fresh seeds were buried in a moist substrate, stored at 10°C to reduce their dormancy level and then gradually heated to 25°C to simulate temperature rising from winter to summer. Seed dormancy level was evaluated at each temperature increase. In a field experiment, seeds were buried for 14 months, with periodic retrievals performed to evaluate seed dormancy level, seed viability and seedling emergence. Results from both experiments revealed that mean summer soil temperatures between 20°C and 25°C induce secondary dormancy in A. hybridus seeds. This dormancy impedes germination at low temperatures and consequently ceases emergence in autumn when soil temperature decreases. The main contribution of this study is to verify that A. hybridus buried seeds are induced into secondary dormancy during the summer and to identify the temperature range that provokes this induction. Integrating this knowledge into weed emergence models can improve predictions of emergence timing, aiding in the development of more effective management strategies.