Ornamental grasses have become exceedingly popular in the United States as a result of gardeners’ acceptance of a more natural landscape appearance and the low maintenance requirements of ornamental grasses (Meyer, 2012). Sales of ornamental grasses in the United States were ≈$124 million in 2009 [U.S. Department of Agriculture (USDA), 2012], up from $61 million in 2003 (Meyer, 2012). With the priority of many federal, state, and local governments to plant native grasses on public land and governmental requirements for native grasses to be planted at sites for oil exploration, pipeline, and mine-site reclamation (Smith and Whalley, 2002), and the acceptance by gardeners of ornamental grasses, sales are increasing in the United States. The ornamental grass little bluestem is now listed as a major U.S. native ornamental grass (Meyer, 2012).
Little bluestem [2n = 4x = 40 (Carman and Hatch, 1982)], a segmental allotetraploid (Deward and Jalal, 1974) formerly known as Andropogon scoparius, is a warm-season perennial bunchgrass found throughout North America (except Nevada and Oregon), southern Canada, and Mexico. Little bluestem is a mycorrhizal plant, associating with Glomus sp. (Anderson et al., 1984), that has a phosphorus requirement that is extremely low (Wuenscher and Gerloff, 1971). Little bluestem is drought-tolerant, displays facultative self-pollination, is morphologically plastic (Fernald, 1950), and forms silvery blue clumps 0.3 to 0.6 m in height. Furthermore, it can show wide variability in height and form. Flowering spikelets are produced in late summer through fall and range in color from blue–green to silvery gold. The uses of little bluestem have been for forage, hay production, range and conservation plantings, erosion control, as a potential lignocellulose biomass feedstock (Gonzalez-Hernandez et al., 2009), and native ornamental grass. No serious insect or disease problems have been reported.
In the past, seeded cultivars of little bluestem were developed for use in pastures and for conservation and include the cultivars Aldous, Badlands Ecotype, Cimmaron, Pastura, Prairie View, and Southlow Michigan. New horticultural marketing programs such as Proven Winners (Meyer, 2012) and web sites promoting native plants have successfully targeted consumers to buy ornamental grasses.
Few genetic or genomic tools are available for little bluestem, although non-sequence-specific random amplified polymorphic DNA [RAPD (Huff et al., 1998)] and amplified fragment length polymorphisms (AFLP) markers (Fu et al., 2004) have been used to assess genetic diversity. Fu et al. (2004) assessed the genetic diversity of six natural populations of little bluestem in Manitoba and Saskatchewan and Huff et al. (1998) assessed genetic variation within and among four populations from New Jersey and Oklahoma. Both studies found that a high proportion of the genetic variability was found within the populations and only a small percentage was represented among populations (Fu et al., 2004; Huff et al., 1998). The authors conclude that the patterns of molecular variation demonstrated by AFLP and RAPD are not associated with geographical origins of the populations. Thus, the genetic variation observed in AFLP and RAPD studies within populations and between individuals may be the result of outcrossing and gene flow through pollen and seed dispersal.
Morphological variation, although easily observed within populations, is not a useful indicator of provenance, habitat, or genetic divergence. From a conservation standpoint, substantial genetic variation could be captured by sampling relatively few individuals from single sites because genetic divergence among natural populations is weak when analyzed with geographic distance (Fu et al., 2004). It is worth noting that the slight but significant differences, observed among populations by Fu et al. (2004) and Huff et al. (1998), are relatively small compared with other outcrossing species (Hamrick and Godt, 1989).
Simple sequence repeat markers, or microsatellites, are repeating DNA sequences of one to six nucleotides that are found in coding and non-coding regions of the genome (Toth et al., 2000). SSR markers, including expressed sequence tag markers, have a wide range of uses such as linkage map development, quantitative trait locus mapping, marker-assisted selection, parentage analysis, cultivar fingerprinting, and genetic diversity studies (Egan et al., 2012). Traditionally SSR development has been completed by creating enriched genomic libraries, mining from databases, and the transfer of SSR markers from closely related species. The use of next-generation sequencing platforms generates thousands of SSRs efficiently and cost-effectively and has been successfully used in warm-season grasses (Harris-Shultz et al., 2013; Mulkey et al., 2013). With the interest in little bluestem, and the horticultural planting of a few recommended cultivars, we aimed to determine ploidy level and to create SSR markers to assess the genetic diversity among the USDA–Agricultural Research Service (ARS) National Plant Germplasm System (NPGS) collection.
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