Environmental control of seed dormancy, germination and seedling emergence of three weed species

Seed germination is a critical event in the success of any weed species. However, germination of weed seeds is conditioned by the presence of dormancy. Dormancy is controlled by genes as influenced by seed developmental processes and by environmental factors. We studied how chilling (12 weeks at 4 C and wet conditions), temperature, temperature fluctuation, and light quality affect the seed dormancy of common waterhemp (Amaranthus tuberculatus (Moq.) J.D. Sauer. synonymous A. rudis J.D. Sauer), giant foxtail (Setaria faberi Herrm.) and velvetleaf (Abutilon theophrasti Medicus). Also we studied how temperature requirements for seed germination can be used for analyzing seedling emergence in artificial and natural seed banks. Chilling did not affect the dormancy level of giant foxtail or velvetleaf seeds. However, common waterhemp seeds reduced dormancy level after chilling and were more responsive to temperature fluctuation and light exposure. Only common waterhemp germination was promoted by exposure to red light (660nm). There was a positive relationship between the amplitude of temperature fluctuation and common waterhemp and giant foxtail germination. Common waterhemp seeds also increased germination rate with increasing amplitude of temperature fluctuation. Temperature requirements for germination cannot alone be used to describe weed emergence in the field. Artificial seed banks showed different emergence patterns of the weed species studied compared to the natural seed banks. The large differences between seed banks were due to soil physical characteristics and seed dormancy level.