Evidence of differences in seed dormancy among populations of Bromus sterilis

Seeds of 40 populations of Bromus sterilis L. were collected in the souther n and midland counties of England over a 2-year period and grown outdoors i n pots in two subsequent years. In the first year, seeds were tested in a 1 2-h dark/12-h light regime at 15 degrees C and in the second year the seeds were tested both in the dark/light regime and in the dark at 15 degrees C. There was a wide range in the degree of enforced dormancy given by the dar k/light regime. Germination of freshly collected seeds in the dark/light re gime after 21 days ranged from 44% to 97% in the populations tested in the first year and from 19% to 97% in populations tested in the second year. In duced dormancy was caused by light in two populations. Seeds had little inn ate dormancy apart from in two populations which gave 64% and 68% germinati on, respectively, in the dark after 21 days. A field trial in which seeds o f a selected range of six populations were sown on the soil surface after h arvest (August 8), showed that populations predicted to be inhibited by lig ht in laboratory tests were also inhibited by light in the field and, depen ding upon the population, there was between 4% and 54% of the seeds remaini ng ungerminated by October 23 in the year of planting. By June of the follo wing year, 36% of the seeds sown on the soil surface in one population stil l remained viable and ungerminated. The agricultural significance of the re sults is discussed.