Nicotiana tabacum L., cv Speight G-28, seeds were separated into seven size groups (354-400, 400-420, 420-447, 447-473, 473-500, 500-532, 532-563, and 563-595µm) with the use of an automated sonic sifter. Sized seeds were pelletized through different commercial sources to give four different pellet types: Normal, Greenhouse, Asgrow and Royal Slius. Pelleted and unpelleted seeds were germinated at 25 or 21 °C. or under varying day/night temperature regimes: 20/15, 22.5/17.5, 25/20, 27.5/22 and 30/25 °C. Under all conditions large seeds fared better than small seeds in terms of both germination time and percentage. Thus difference was most obvious between seeds representing two extreme size-groups. Pelletization delayed the germination rate without affecting germination percentage, and appeared to be protective against thermal stress as compared to uncoated seeds. Asgrow and Royal Sluis pellets germinated faster than Normal and Greenhouse pellets whereas the latter two provided greater protection against thermal stress. No interaction could be detected between seed size and pellet type. It appears that the disintegration time for various pellets suspended in free water can be used as a quick and reliable indicator of their germination potential before time consuming studies are undertaken.

(Full article published with kind permission from "Tobacco International")