Weedy Adaptation in Setaria spp. IV. Changes in the Germinative Capacity of S. faberii (Poaceae) Embryos with Development from Anthesis to After Abscission

Abstract

Studies were conducted evaluating germinability states in giant foxtail (Setaria faberii) embryos, as well as surrounding tissues (hull, caryopsis), with germination assays. Further, seed age, fascicle arrangement, flowering patterns, and elongation in the inflorescence were evaluated. Both qualitatitive and quantitative morphological observations of the hull and the caryopsis were revealed by precisely determined fertilized spikelet age from anthesis until after seed abscission. Red coloration of the placental pad at ≈ 11 d after anthesis is probably a morphological indicator of physiological maturity. Germinability of giant foxtail embryos changed with development. Four qualitatively different types of embryo germination were observed during development of the seed: early disorganized callus growth at the basal, coleorhizal end of the embryo; germination of immature embryos with shortened and thickened axes; germination of the scutellum; and germination and growth of the coleoptile and coleorhiza in embryos aged 7 d after anthesis and older. Axis-specific embryo germinability was also observed. Inhibition of the embryo could be localized to the coleoptile, the coleorhiza, or both. These studies provide evidence for a complex model of germinability regulation based on the independent, asynchronous actions of the embryo, caryopsis, and hull compartments, as well as on their dependent, synchronous action. These studies provide evidence for a dynamic, developmental model of giant foxtail germinability regulation resulting in phenotypes with a wide range of germinability shed from an individual panicle. These diverse germinability phenotypes are found at all stages of development, but particularly when the seed is shed and the soil seed bank is replenished.