Plant emergence of PEG-osmoprimed seeds under suboptimal temperatures in two cultivars of sweet sorghum differing in seed tannin content.

The effect of polyethylene glycol (PEG) osmopriming on plant emergence inlaboratory at optimal (25 C) and suboptimal (18 and 14 C) temperatureswas assessed in two cultivars of sweet sorghum differing in kernel colour:Brandes, light-coloured, and Roce, dark-coloured. Sterilized sand or non-sterilizedsoil were used as substrates. PEG osmopriming enhanced seedling emergencein sand. In soil, the light-seeded cultivar produced seedlings only atoptimum temperature, whereas the unprimed dark-seeded cultivar performedwell as in sand at all temperatures and reduced dramatically its germinationcapacity at suboptimal temperatures following priming treatment. These resultsmight be related to the presence of tannins in the seed coat. Seed tannin contentsof 80 and 590 mg 100 g)1 seed fresh weight (FW) were determined inBrandes and Roce respectively. These amounts consistently reduced after PEGosmopriming, especially in Roce (217.5 mg 100 g)1 seed FW). The decline intannin content in Roce, because of osmopriming, might explain the poor emergenceof this cultivar in soil. These results suggest the opportunity of usinghigh-tannin cultivars of sweet sorghum in the field, which may better growthin this environment when early sowings are required.