Responses of Stokes Aster Achenes to Chilling

Stokes aster [ Stokesia laevis Hill (Greene)] is a perennial ornamental; achenes are a prospective source of vernolic acid for the chemical industry. Responses of achenes of 6 Stokes aster accessions to temperatures of 0° to 20°C were studied. There was no germination below 11°; germination was near 0 at 11° and reached a maximum at 20°. Achenes equilibrated at 15% moisture generally germinated more rapidly than those at 5% moisture. In hydration-chilling experiments, more than one day of exposure to chilling prior to germination decreased germination and increased the frequency of abnormal seedlings in some entries. Equilibration at 15% moisture prior to chilling reduced damage slightly compared to 5% moisture. There seemed to be a direct relationship between early imbibition rate and susceptibility to chilling damage. Gradual chilling and warming of germinated achenes resulted in a significant reduction in damage compared to abrupt chilling and warming.