Annual changes in temperature and light requirements for Ipomoea purpurea seed germination with after-ripening in the field following dispersal

Field and laboratory experiments were conducted in SC, USA, in 2004/2005 and 2006/2007 to determine the effect of temperature, light, and spring burial on Ipomoea purpurea (L.) Roth. seed germination over a 12-month period after seed maturation in the field. The seed collections used for the temperature and light studies had physical dormancy (water-impermeable), with 10-23% and 17-46% germination, respectively, of the freshly matured viable seeds. Freshly matured seeds used for the temperature study germinated to higher percentages at 15-25 °C constant. During winter (3 months after seed maturation), seed germination was higher at 30 °C constant or 22.5/37.5 °C fluctuating. During spring (6 months after seed maturation), there was a widening of thermal range (10-40 °C constant or 2.5/17.5 to 27.5/42.5 °C fluctuating) for germination. Germination of surface-lying or buried seeds was higher at 35-40 °C constant or 22.5/37.5-27.5/42.5 °C fluctuating in late summer (9 months after maturation) and autumn (12 months after maturation). Light had minimal influence on germination of surface or buried seeds of the tested population over the 12-month after-ripening period. A temperature-mediated annual dormancy continuum of I. purpurea seed has been proposed in this research, which will contribute to the development of weed emergence models aimed at improving strategies for I. purpurea control in the field.