TEMPORAL CHANGES IN VELVETLEAF (ABUTILON-THEOPHRASTI) SEED DORMANCY

Primary physical dormancy caused by seed coat impermeability to water is a major reason for the persistence of velvetleaf in soil seedbanks. Understanding temporal trends in seed dormancy status will help predi ct potential emergence in the spring. Experiments were begun in 1992 a nd 1993 to determine the effects of velvetleaf seed maturation time, s torage environment, and storage duration on changes in seed dormancy a nd germination over 20 mo. Seeds buried 1 and 10 cm deep exhibited a 3 0 to 70% decline in physical dormancy from maturity until winter, litt le change in dormancy from winter through the following summer, and a further decline the next autumn. The loss of physical dormancy was mor e rapid for early than for late maturing seeds and more rapid in 1992 than in 1993. Physical dormancy of seeds held at 4 C declined steadily , at a rate of approximately 0.8% per day, over the course of the stud y. Germination of seeds buried 1 cm averaged 23 to 37% in the first sp ring after harvest, which was equivalent to 68 to 100% of seeds that h ad lost physical dormancy over autumn and winter. The percentage of se eds with enforced dormancy reflected the loss of physical dormancy dur ing autumn and the loss of seeds to germination during spring and summ er. Additional information on how autumn temperature and moisture cond itions influence the pattern of dormancy decline could aid in explaini ng the variation in velvetleaf infestations over time.