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 greater-than-or-equal-to 85% wa s achieved after 3,2, or 1 day of irradiance at 1.5, 15, or 75 mumol.s -1.m-2, respectively. Keeping imbibed seeds in darkness for greater-th an-or-equal-to 2 days before light exposure caused reduced total germi nation percentages (G), delayed achieving 50 % of the final germinatio n percentage (T50), and increased the days between 10% and 90% germina tion (T90-T10). Light for 6 hours daily at 1.5, 15, or 150 mumol.s-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. Es timated rates of decline (increase) in G, T50, or T90 - T10 with each added day of light (darkness) or increasing daily hours of fight were measured by fitting regression equations. Impatiens seed germination w as promoted by the initial 1 to 3 days of light, but light inhibited r adicle extension in the latter germination stages.