Characterization of foxtail (Setaria spp) seed production and giant foxtail (S faberi) seed dormancy at abscission
The foxtails are cosmopolitan weeds and among the most troublesome in agriculture. High seed production and seed dormancy are important attributes contributing to the success of the foxtails as weeds. The amount and sources of germination variability among giant foxtail seed were evaluated. Seed from a single genetic line of giant foxtail was grown under field, greenhouse and growth chamber conditions. Germination assays were conducted at abscission and following stratification and seed dissection. Most giant foxtail seed were shed dormant. As the seed rain progressed, mean germination percentage and variability in the germination requirements among samples increased. Changes in seed dormancy were associated with biological and environmental parameters. Within an individual panicle, seed that developed later were more likely to germinate than those that developed earlier. Seed from panicles that developed relatively later on a plant were also more likely to germinate than seed from panicles that developed earlier. Seed grown in the field were less dormant than those grown in the greenhouse which were in turn less dormant than those from growth chamber conditions. It is possible that each seed has an individual germination requirement. Seed from giant, green and yellow foxtail panicles were collected throughout the reproductive period. A higher number of seed was found than has been generally reported. Although seed number per panicle, panicle length and seed density (seed number per unit panicle length) varied among foxtail species, panicles and sites, some consistent relationships were found. The relationship between seed number and panicle length also varied among foxtail species, panicles and sites. The giant foxtail germination process was divided into three axis specific embryo growth states. Photographic evidence of each germination state is shown for both caryopses and seed. The germination state after eight to twelve days under germination conditions is believed to reveal the potential for germination possessed by the seed prior to germination.