Weedy Adaptation in Setaria spp.: VII. Seed Germination Heteroblasty in Setaria faberi

The dormancy status of S. faberi seed at abscission was assessed with reference to tiller and panicle development. Seed from a single genetic line were grown under field, greenhouse and controlled environment growth chamber conditions. At abscission, a small fraction (<10%) of S. faberi seed germinated under favorable conditions. Seed were dissected and germination of caryopses and embryos also tested. Removal of seed structures exterior to the embryo increased percentage germination. As the seed rain progressed mean percentage germination and variation among samples increased. Changes in germination were correlated with tiller development and relative time of seed maturity within a panicle. Seed produced on tillers that developed earlier were more likely to be dormant than seed from later-developing tillers. Seed that matured later on a panicle were more likely to germinate than seed that matured earlier on the same panicle. A consistent trend toward later maturing seed having less dormancy was found for seed grown under different environments which implies an inherent or parental source for variation in giant foxtail seed dormancy. The variation in percentage germination at abscission and following stratification treatments indicates that the S. faberi seed rain consists of individual seeds, possibly each with a different degree of dormancy.