Germination behaviour of dormant oilseed rape seeds in relation to temperature

Seeds of oilseed rape (Brassica napus L., cv. Liglandor) were induced into secondary dormancy by imbibing them for 2-4 weeks in an osmotic solution at -1500 kPa in darkness. Treated seeds were then transferred into pots or Petri dishes, where they were given adequate water for germination. These pots and Petri dishes were exposed to various temperature regimes during the course of the following 6-14 months. During that time, seed samples were taken at 2- to 6-weekly intervals to monitor survival of seeds and to study their dormancy. The number of seeds that had not germinated in pots or Petri dishes remained constant in the majority of treatments, but it declined when seeds were exposed to pronounced daily temperature alternations. This decline was due to germination and not to death of seeds from other causes. Germination tests on subsamples of seeds showed that they were light sensitive, more seeds germinating in the light than in the dark. The seeds' germination behaviour differed between sampling dates. This variation in germination behaviour appeared not to display the classical dormancy:non-dormancy cycle. Part of the variation seemed to be due to the changes in temperature that the seeds experienced when taken from pots and set up in the germination tests. Seeds exposed to a constant temperature for 1 year appeared to become more dormant with time. The relevance of this work in relation to the persistence of volunteer oilseed rape is discussed.