Light Governs the Germination of Impatiens wallerana Hook. f. Seed

The role of light on impatiens seed germination and radicle emergence was studied. Seeds having a photodormancy require light for only part of the germination period. Germination ≥85% was achieved after 3, 2, or 1 day of irradiance at 1.5, 15, or 75 μmols -1 •m -2 , respectively. Keeping imbibed seeds in darkness for ≥2 days before light exposure caused reduced total germination percentages (G), delayed achieving 50% of the final germination percentage (T50), and increased the days between 10% and 90% germination (T90 - T 10). Light for 6 hours daily at 1.5, 15, or 150 μmols -1 •m -2 promoted high G and rapid and uniform germination, but daily 12 to 24 hours of irradiance decreased G and increased T50 and T90 - T10. Estimated rates of decline (increase) in G, T 50, or T90 - T10 with each added day of light (darkness) or increasing daily hours of light were measured by fitting regression equations. Impatiens seed germination was promoted by the initial 1 to 3 days of light, but light inhibited radicle extension in the latter germination stages.