Responses of Vegetable Seeds to Controlled Hydration

Abstract

Leek, onion and carrot seeds were imbibed in water and in solutions of polyethylene glycol (PEG) 6000 over the range −0.5 to −4.0 MPa osmotic potential, for periods up to 28 d at 15 °C. Seeds started to germinate after 7 and 14 d at −0.5 MPa and −1.0 MPa PEG, respectively, but in the latter case, germination did not exceed 5%. No germination occurred in solutions of lower (more negative) osmotic potential. Seed moisture content increased with osmotic potential in all three species and the relationships were unaffected by the duration of imbibition in solutions of −1.0 to −4.0 MPa, though leek seeds had higher moisture contents than the other species for any given osmotic potential. Linear relationships between response to priming (difference between mean germination times of primed and untreated seeds) and seed moisture content were obtained for each species, positive responses being obtained above 30–35% seed moisture content with optima at 46, 44.5 and 44% seed moisture contents in leek, onion and carrot, respectively. Priming had no effect on embryo volume or cell number per embryo in leek and onion. Carrot embryo volume increased by 43% and cell number per embryo doubled in primed compared with untreated seeds, whereas seeds imbibed in water showed only a slight increase in cell number per embryo at the stage when radicles were beginning to penetrate the seed coat.