Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/21/2003
Publication Date: 7/1/2003
Citation: SMART, A.J., VOGEL, K.P., MOSER, L.E., STROUP, W.W. DIVERGENT SELECTION FOR SEEDLING TILLER NUMBER IN BIG BLUESTEM AND SWITCHGRASS. CROP SCIENCE. 2003. 42:1427-1433. Interpretive Summary: Genetically improving the seedling vigor of pasture and range grasses would improve the ability of land managers to rapidly and successfully establish seeded pastures and rangeland. Grass seedling tiller number and shoot weight are traits associated with seedling vigor. Two generations of divergent selection for seedling tiller number and seedling shoot weight in the North American prairie grasses, big bluestem and switchgrass, resulted in significant changes in the tiller demographics of the selected populations. Selection for multi-tillers at the seedling stage and intermating selected plants for two generations produced switchgrass and big bluestem populations with seedlings that had significantly more tillers at the seedling stage than the parent source populations. Selection for seedlings with single, large tillers at the seedling stage produced populations with single or few large seedling tillers. Field evaluation trials need to be conducted to determine the effect of these changes on field establishment and forage yields and quality. It is anticipated that the single tiller populations may be more suitable for use in biomass production systems while the multi-tiller populations may be more suitable for use in grazing systems.
Technical Abstract: Grass seedling tiller number and shoot weight are traits associated with seedling vigor. The response to selection for high shoot weight and divergent selection for seedling tiller number in big bluestem (Andropogon gerardii Vitman) and switchgrass (Panicum virgatum L.) seedlings and realized heritability was determined for these traits. The base populations, which were breeding populations of `Pawnee¿ big bluestem and `Pathfinder¿ switchgrass, were seeded in approximately 2000 cone-tainer cells in winter 1996. Divergent selection for seedling tiller number was accomplished by stratified selection of the 100 heaviest seedlings (based on fresh weight) that had a single or multiple (three or more) tiller(s) 6 to 8 wk after planting. This produced four populations [big bluestem high seedling weight, multiple tiller (BBMT), big bluestem high seedling weight, single tiller (BBST), switchgrass high seedling weight, multiple tiller (SWMT), and switchgrass high seedling weight, single tiller (SWST)] which were planted in isolated polycross nurseries. Seed from the polycross nurseries was used to conduct a second cycle of selection. In 1999 and 2000, the base population and populations produced by the two cycles of selection were evaluated in greenhouse studies for fresh weight and tiller number. Realized heritability and gain per cycle of selection were determined. Seedling fresh weight was increased in BBST and SWST cycle 2 populations and divergent selection for tiller number resulted in populations significantly different from the base population. Realized heritability estimates for seedling tiller number in big bluestem and switchgrass were 0.26 and 0.23, respectively. The effect of genetic modification of seedling tiller number and shoot weight on establishment under field conditions and on mature plant phenotypes will need to be determined.