LARGE SUNFLOWER SEEDS ARE CHARACTERIZED BY LOW EMBRYO VIGOR

The cause for the differences in germination ability of large and smal l confection sunflower (Helianthus annuus L.) seeds was investigated o ver 3 years. The source-sink relationship was manipulated to better ex plore the differences between seeds of various sizes and to study the role of the embryo and the pericarp (hull) in controlling germination ability. Percent germination of large seeds was significantly lower th an that of small seeds when tests were performed at 15 degrees C. Incr easing the ratio of leaf area to number of developing seeds caused an increase in mean seed mass, but resulted in a lower percentage of germ ination. Seed vigor, as measured by mean time to germination or to eme rgence of hulled seeds or by rate of root elongation, was negatively c orrelated with embryo mass, indicating that the low vigor of large see ds is not due to the mechanical barrier imposed by the hull, Analysis of electrolyte leakage confirmed the hypothesis that the low quality o f large seeds results from a disturbance during the process of seed de velopment.