Latitudinal Adaptation of Switchgrass Populations

random genetic drift, mutation, and natural selection combined with environmental variation due to latitude, Switchgrass (Panicum virgatum L.) is a widely adapted warmaltitude, soil type, and precipitation have resulted in season perennial that has considerable potential as a biofuel crop. significant genetic and phenotypic variation in switchEvolutionary processes and environmental factors have combined grass. Switchgrass has a ploidy series from 2n 2x to create considerable ecotypic differentiation in switchgrass. The objective of this study was to determine the nature of population 18 to 2n 12x 108 (Nielsen, 1944) and two distinct location interaction for switchgrass, quantifying potential differences cytotypes, upland and lowland (Hultquist et al., 1996). in latitudinal adaptation of switchgrass populations. Twenty populaUpland and lowland cytotypes tend to be genetically tions were evaluated for biofuel and agronomic traits for 2 yr at five and phenotypically distinct from each other (Gunter et locations ranging from 36 to 46 N lat. Biomass yield, survival, and al., 1996; Sanderson et al., 1996). Latitude-of-origin has a plant height had considerable population location interaction, much large impact on productivity and survival of switchgrass of which (53–65%) could be attributed to the linear effect of latitude strains that are evaluated in extreme environments, such and to germplasm groups (Northern Upland, Southern Upland, Northas eastern Texas (Sanderson et al., 1999), suggesting ern Lowland, and Southern Lowland). Differences among populations genetic variation in adaptation. Genetic responses to were consistent across locations for maturity, dry matter, and lodging. latitude may be complex, resulting from genetic variaIncreasingly later maturity and the more rapid stem elongation rate of more southern-origin ecotypes (mainly lowland cytotypes) resulted tion for photoperiodism, cold tolerance, or heat tolin high biomass yield potential, reduced dry matter concentration, and erance. longer retention of photosynthetically active tissue at more southern Despite the spread and duration of agriculture in eastlocations. Conversely, increasing cold tolerance of more northernern North America, there remain hundreds of remnant origin ecotypes (mainly upland cytotypes) resulted in higher survival, prairie sites, protected by public or private organizations stand longevity, and sustained biomass yields at more northern loca(Hopkins et al., 1995b; Hultquist et al., 1997). Most tions, allowing switchgrass to thrive at cold, northern latitudes. Alswitchgrass cultivars are either seed increases of sourcethough cytotype explained much of the variation among populations identified collections or products of a limited number and the population location interaction, ecotypic differentiation of breeding cycles tracing to many of these remnant within cytotypes accounted for considerable variation in adaption of prairie sites (Alderson and Sharp, 1994). Intensive selecswitchgrass populations. tion and breeding of switchgrass began only during the last quarter of the 20th century (Moser and Vogel, 1995). Thus, the variability present among most cultivars and S is a widely adapted warm-season perenecotypes should largely reflect natural variation for adnial that has considerable potential as a biofuel crop. aptation to specific climatic and edaphic conditions unSwitchgrass can produce a high yield of biomass across a der which these local populations evolved. wide geographic range; it is suitable for use on marginal, The objective of this study was to determine the nahighly erodible, and droughty soils; it has the potential ture of population location interaction for agronomic of sequestering large amounts of atmospheric carbon in and biofuel traits of switchgrass, quantifying potential permanent grasslands; and it provides excellent nesting differences in latitudinal adaptation of switchgrass pophabitat for migratory birds (Moser and Vogel, 1995; ulations. Paine et al., 1996; Sanderson et al., 1996). The combination of heat, cold, and drought tolerance within the MATERIALS AND METHODS species results in an adequate level of adaptation for nearly all ecosystems east of the Rocky Mountains and Twenty switchgrass populations, originating from Texas to south of Hudson Bay, including arid conditions in the South Dakota (Table 1), were planted at five locations in shortgrass prairie to marshland and open woodland spring 1998. Plot sizes were 1.4 1.7 m at Spooner, WI (45 49 N, 91 54 W); 1.7 1.8 m at Arlington, WI (43 20 N, 89 23 (Hitchcock, 1951). W); 1.5 3.8 m at Mead, NE (41 13 N, 96 29 W); 1.5 Evolutionary processes including gene migration, 3.4 m at Manhattan, KS (39 25 N, 96 35 W); and 1.5 4.6 m at Stillwater, OK (36 7 N, 96 5 W). Soil types were Omega loamy sand (sandy, mixed, frigid Typic Haplorthod) at M.D. Casler, USDA-ARS, U.S. Dairy Forage Research Center, Madison, WI 53706-1108; K.P. Vogel, USDA-ARS, 344 Keim Hall, Univ. Spooner, Plano silt loam (fine-silty, mixed, superactive, mesic of Nebraska, P.O. Box No. 830937, Lincoln, NE 68583-0937; C.M. Typic Argiudoll) at Arlington, Sharpsburg silt loam (fine, Taliaferro, Dep. of Plant and Soil Sci., Oklahoma State Univ., Stillwasmectitic, mesic Typic Argiudoll) at Mead, Haynie very fine ter, OK 74078-6028; R.L. Wynia, USDA-NRCS, Plant Materials Censandy loam (coarse-silty, mixed, superactive, calcareous, mesic ter, 3800 S. 20th St., Manhattan, KS 66502. This research was funded Mollic Udifluvent) at Manhattan, and Kirkland silt loam (fine, in part by the U.S. Dep. of Energy Biomass Fuels Program via the mixed, superactive, thermic Udertic Paleustoll) at Stillwater. Oak Ridge National Lab. Contract No. DE-A105-900R2194. Received Plots were seeded at a rate of 400 pure live seed m . The 5 Mar. 2003. *Corresponding author ([email protected]). experimental design at each location was a randomized comPublished in Crop Sci. 44:293–303 (2004).  Crop Science Society of America Abbreviations: ADL, acid detergent lignin; IVDMD, in vitro dry matter digestibility; NDF, neutral detergent fiber. 677 S. Segoe Rd., Madison, WI 53711 USA