VARIATION IN SEED DORMANCY AMONG MOTHER PLANTS, POPULATIONS AND YEARSOF SEED COLLECTION

Variation in dormancy level was tested in seeds of four species, each collected from three populations in 1994 and 1995 (experiment 1). Germ ination was tested in light and darkness on recently-harvested seeds a nd on those after-ripened in dry storage for one year. In addition, se eds from each of eight individual plants within each of eight populati ons were tested for germination when recently harvested and after warm stratification or cold stratification followed by a drying period (ex periment 2). Seeds from the two years differed in dormancy level in Si lene noctiflora, Sinapis arvensis and Spergula arvensis. Germination p ercentage differed significantly among populations in Sinapis arvensis and Spergula arvensis in both experiments and in Thlaspi arvense in e xperiment 2. Furthermore, dormancy level in seeds from different mothe r plants also varied in the three species tested in experiment 2. Vari ations at the three levels tested (year, population and mother plant) indicate that these species have a random pattern of variation in dorm ancy level. It is concluded that variation in seed dormancy among moth er plants, populations and years must be taken into account when testi ng the germination characteristics of a species and also when attempti ng to model weed seed bank dynamics.