Induction of secondary dormancy in rape seeds (Brassica napus L) by prolonged imbibition under conditions of water stress or oxygen deficiency in darkness

Prolonged imbibition under conditions of water stress or oxygen deficiency can lead to the induction of secondary dormancy in rape seeds. During imbibition in darkness seeds develop light sensitivity. The percentage of seeds not germinating in the dark depends on various factors prevailing during and after the stress treatment, as well as on the intrinsic susceptibility of the seeds to these factors. In experiments on the effect of water stress it was found that the percentage of secondary dormant seeds could be increased in the range of 0-75%, by greater water suction and duration of imbibition of the seeds. Additionally, there were indications that increasing treatment temperature resulted in increasing percentages of dormant seeds. However, fewer secondary dormant seeds were produced when treatment temperature and test temperature differed greatly from each other. Experiments on the effect of oxygen deficiency also revealed a positive effect of treatment duration. The general degree of dormancy induction, however, in this series of experiments was low. At 20 degrees C almost no dormancy induction was observed, whilst at 12 degrees C there were between 0 and 30% dormant seeds. Genotypic differences previously assessed in model experiments with buried seeds were confirmed in both studies. Oilseed rape cultivars Bienvenu and Liglandor were shown to be able to build up high percentages of secondary dormant seeds, whereas cultivars Jet Neuf and Falcon had a rather low susceptibility towards the dormancy imposing factors tested. Cultivar Rubin was intermediate in response. There was often much variation between experiments with the same experimental design. The reasons for this are unclear. (C) 1997 Elsevier Science B.V.