Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/8/2005
Publication Date: 12/15/2006
Citation: Boe, A.R., Casler, M.D. 2006. Hierarchical analysis of switchgrass morphology. Crop Science. 45:2465-2472. Interpretive Summary: Switchgrass is an important forage, conservation, and potential biomass crop in the eastern USA and Canada. We conducted a detailed analysis of stem structure for eight varieties of diverse genetic and geographic origin. Our data provided a basis for understanding morphological variation among varieties and developing strategies for improving populations for biomass production, conservation, and wildlife habitat in the Northern Plains and Great Lakes regions. Because the number of nodes per stem is constant within varieties, genetic improvement for biomass production will rely on genetic variation for number of stems and size of stems. Since selection for higher yield of individual plants has not usually been successful for improving yield in swards for perennial grasses, selection for a morphological trait that exhibits extensive genetic variation should be considered. These results are important to agronomists and plant breeders working with switchgrass for forage, biomass, and conservation purposes.
Technical Abstract: Switchgrass (Panicum virgatum L.) is an important forage, conservation, and potential biomass crop east of the 100th meridian in the USA and Canada. Our objective was to determine the importance of genetic variation and phenotypic plasticity at the cultivar level in the expression of morphological traits that influence biomass production in swards, tillers, and phytomers. Eight genetically diverse cultivars ranging in areas of origin from 38°N 88°W (Cave-In-Rock) to 46°N 102°W (Dacotah) were harvested during September 2000 in 1-, and 3-yr-old swards in eastern South Dakota and Wisconsin and during September 2000 and 2001 in 15-yr-old swards in central South Dakota for biomass, tiller density, contribution of reproductive tillers to sward population and biomass, tiller weight, number of aerial phytomers reproductive tiller-1, blade, sheath, internode, and inflorescence components of tiller weight, and weight of leaf and stem fractions of individual aerial phytomers of reproductive tillers. Genetic variation among cultivars was found for morphological traits descriptive of swards (i.e., biomass and tiller density) and tillers (i.e., tiller weight, phytomer number tiller-1, and leaf, stem, internode, and inflorescence fractions of reproductive tillers). Cultivars of southern origin (i.e., Cave-In-Rock, Shawnee, and Trailblazer) produced larger amounts of biomass (13 Mg ha-1) than cultivars of northern origin (i.e., Dacotah and Forestburg) (7 Mg ha-1) averaged across four environments in SD and one in WI. Tiller density was highest for Dacotah (1090 tillers m-2) and lowest for Cave-In-Rock (520 tillers m-2). Number of phytomers reproductive tiller-1 ranged from 5.2 for Dacotah to 7.4 for Cave-In-Rock. Weights of reproductive tillers ranged from 0.7 g for Dacotah to 3.4 g for Cave-In-Rock. The proportion of tillers that reached reproductive development was highly sensitive to environmental variation, and individual aerial phytomers in reproductive tillers also exhibited high levels of plasticity, with 4-fold differences between weights of internodes for corresponding phytomers from tillers in swards in WI and SD. Data from this study provided a hierarchical basis for understanding genetic and phenotypically plastic variation in morphological characteristics that influence biomass production and distribution among aerial organs in switchgrass.