Application of the hydrotime model to assess seed priming effects on the germination of rapeseed (Brassica napus L.) in response to water stress

Our aim was to determine whether the parameters of the hydrotime model can be used to compare the effects of seed priming treatments on germination. Seeds of three rapeseed cultivars ('H61', 'H4815', and 'DK003') were exposed to priming treatments and then their germination was tested at different water potentials. Seed priming improved the germination percentage, which was higher in 'H4815' than in the other two cultivars, and it increased germination rate (decreased theta(H)) and uniformity (decreased sigma(psi b)). The increase in germination rate was higher in PEG-osmoprimed than in NaCl-osmoprimed and hydroprimed seeds. The base water potential allowing 50% germination (Psi(b(50))) also was affected by seed priming, but the response of cultivars to different priming treatments varied. Compared with the control seeds, hydropriming of 'H61' seeds shifted psi(b(50)) toward negative values, whereas NaCl-osmopriming of 'H4815' seeds shifted psi(b(50)) toward negative values. On the other hand, priming of 'DK003' seeds shifted psi(b(50)) to more positive values and increased susceptibility to water stress. After dormancy-breaking and dormancy-induction treatments, psi(b(50)) shifted to more negative or positive values, indicating the release of primary dormancy and induction of dormancy, respectively. Therefore, priming treatments should be selected, depending on the environmental conditions anticipated to prevail during the germination of rapeseed seeds.