Competitive effects of cultivar and wild switchgrass on other native grasses

There is mounting concern that selection and breeding of native grasses for greater biomass production could promote weediness. Yet little is known about the invasion potential or ecological impacts of such selectively bred native grasses. Here we focus on cultivars of native switchgrass (Panicum virgatum L.) that have undergone selection, breeding, and intraspecific hybridization to improve agronomic traits for biomass production. We evaluated the competitive effects of switchgrass cultivars (EG-2101 and ‘Trailblazer’) and wild switchgrass populations on two native prairie grasses [sideoats grama, Bouteloua curtipendula (Michx.) Torr., and Canada wild rye, Elymus canadensis L.] across a gradient of switchgrass density in a greenhouse. Cultivars produced 48–128% more biomass and reduced sideoats grama biomass by 25–59% more than wild switchgrass. Effects of switchgrass cultivars on Canada wild rye were minimal compared to sideoats grama. Later flowering and larger seed size of cultivars may be contributing to their greater biomass and competitive effects on sideoats grama. These data suggest that breeding switchgrass for enhanced biomass yield may increase competitive effects on some native grasses. Further studies are merited to test the potential for switchgrass biomass cultivars to spread and impact species diversity of restored and remnant native plant communities.     

Do Cultivated Varieties of Native Plants Have the Ability to Outperform Their Wild Relatives?

Vast amounts of cultivars of native plants are annually introduced into the semi-natural range of their wild relatives for re-vegetation and restoration. As cultivars are often selected towards enhanced biomass production and might transfer these traits into wild relatives by hybridization, it is suggested that cultivars and the wild × cultivar hybrids are competitively superior to their wild relatives. The release of such varieties may therefore result in unintended changes in native vegetation. In this study we examined for two species frequently used in re-vegetation (Plantago lanceolata and Lotus corniculatus) whether cultivars and artificially generated intra-specific wild × cultivar hybrids may produce a higher vegetative and generative biomass than their wilds. For that purpose a competition experiment was conducted for two growing seasons in a common garden. Every plant type was growing (a.) alone, (b.) in pairwise combination with a similar plant type and (c.) in pairwise interaction with a different plant type. When competing with wilds cultivars of both species showed larger biomass production than their wilds in the first year only and hybrids showed larger biomass production than their wild relatives in both study years. As biomass production is an important factor determining fitness and competitive ability, we conclude that cultivars and hybrids are competitively superior their wild relatives. However, cultivars of both species experienced large fitness reductions (nearly complete mortality in L. corniculatus) due to local climatic conditions. We conclude that cultivars are good competitors only as long as they are not subjected to stressful environmental factors. As hybrids seemed to inherit both the ability to cope with the local climatic conditions from their wild parents as well as the enhanced competitive strength from their cultivars, we regard them as strong competitors and assume that they are able to outperform their wilds at least over the short-term.     

Local adaptation of switchgrass drives trait relations to yield and differential responses to climate and soil environments

Switchgrass, a potential biofuel crop, is a genetically diverse species with phenotypic plasticity enabling it to grow in a range of environments. Two primary divergent ecotypes, uplands and lowlands, exhibit trait combinations representative of acquisitive and conservative growth allocation strategies, respectively. Whether these ecotypes respond differently to various types of environmental drivers remains unclear but is crucial to understanding how switchgrass varieties will respond to climate change. We grew two upland, two lowland, and two intermediate/hybrid cultivars of switchgrass at three sites along a latitudinal gradient in the central United States. Over a 4-year period, we measured plant functional traits and biomass yields and evaluated genotype-by-environment (G × E) interaction effects by analyzing switchgrass responses to soil and climate variables. We found substantial evidence of G × E interactions on biomass yield, primarily due to deviations in the response of the southern lowland cultivar Alamo, which produced more biomass in hotter and drier environments relative to other cultivars. While lowland cultivars had the highest potential for yield, their yields were more variable year-to-year compared to other cultivars, suggesting greater sensitivity to environmental perturbations. Models comparing soil and climate principal components as explanatory variables revealed soil properties, especially nutrients, to be most effective at predicting switchgrass biomass yield. Also, positive correlations between biomass yield and conservative plant traits, such as high stem mass and tiller height,  became stronger at lower latitudes where the climate is hotter and drier, regardless of ecotype. Lowland cultivars, however, showed a greater predisposition to exhibit these conservative traits. These results suggest switchgrass trait allocation trade-offs that prioritize aboveground biomass production are more tightly associated in hot, dry environments and that lowland cultivars may exhibit a more specialized strategy relative to other cultivars. Altogether, this research provides essential knowledge for improving the viability of switchgrass as a biofuel crop.     

Modification of native grasses for biofuel production may increase virus susceptibility

Bioenergy production is driving modifications to native plant species for use as novel biofuel crops. Key aims are to increase crop growth rates and to enhance conversion efficiency by reducing biomass recalcitrance to digestion. However, selection for these biofuel‐valuable traits has potential to compromise plant defenses and alter interactions with pests and pathogens. Insect‐vectored plant viruses are of particular concern because perennial crops have potential to serve as virus reservoirs that influence regional disease dynamics. In this study, we examined relationships between growth rates and biomass recalcitrance in five switchgrass (Panicum virgatum) populations, ranging from near‐wildtype to highly selected cultivars, in a common garden trial. We measured biomass accumulation rates and assayed foliage for acid detergent lignin, neutral detergent fiber, in vitro neutral detergent fiber digestibility and in vitro true dry matter digestibility. We then evaluated relationships between these traits and susceptibility to a widely distributed group of aphid‐transmitted Poaceae viruses (Luteoviridae: Barley and cereal yellow dwarf viruses, B/CYDVs). Virus infection rates and prevalence were assayed with RT‐PCR in the common garden, in greenhouse inoculation trials, and in previously established switchgrass stands across a 300‐km transect in Michigan, USA. Aphid host preferences were quantified in a series of arena host choice tests with field‐grown foliage. Contrary to expectations, biomass accumulation rates and foliar digestibility were not strongly linked in switchgrass populations we examined, and largely represented two different trait axes. Natural B/CYDV prevalence in established switchgrass stands ranged from 0% to 28%. In experiments, susceptibility varied notably among switchgrass populations and was more strongly predicted by potential biomass accumulation rates than by foliar digestibility; highly selected, productive cultivars were most virus‐susceptible and most preferred by aphids. Evaluation and mitigation of virus susceptibility of new biofuel crops is recommended to avert possible unintended consequences of biofuel production on regional pathogen dynamics.     

Testing the cultivar vigor hypothesis: comparisons of the competitive ability of wild and cultivated populations of Pascopyrum smithii along a restoration chronosequence

Restoration practitioners often rely on seeds of widely available cultivars representing native species but nonlocal germplasm. Cultivation improves the supply of plant materials and minimizes revegetation costs, but can also favor agronomic traits, and resulting vigor may affect the competitive ability and long‐term persistence of cultivated genotypes at restoration sites. We compared cultivated, restored, and wild populations of Pascopyrum smithii (western wheatgrass) in a greenhouse study to test the extent to which cultivars outcompete local plants in biomass production, and to determine if morphological differences (including height and number of leaves) among cultivated and wild populations persist at restoration sites over time. We found evidence of vigor and greater competitive ability of cultivars in seed mass, growth rate, plant height, and biomass and this advantage occurred when plants were grown alone or in competition with other seed sources. Cultivar vigor persisted at restoration sites over 30 years, but restored populations more closely resembled wild, local populations when cultivars were planted in closer proximity to nearby undisturbed sites. This study supports the cultivar vigor hypothesis and provides evidence for the long‐term persistence of cultivated traits in the environment.     

Genotypic diversity effects on biomass production in native perennial bioenergy cropping systems

The perennial grass species that are being developed as biomass feedstock crops harbor extensive genotypic diversity, but the effects of this diversity on biomass production are not well understood. We investigated the effects of genotypic diversity in switchgrass (Panicum virgatum) and big bluestem (Andropogon gerardii) on perennial biomass cropping systems in two experiments conducted over 2008–2014 at a 5.4‐ha fertile field site in northeastern Illinois, USA. We varied levels of switchgrass and big bluestem genotypic diversity using various local and nonlocal cultivars – under low or high species diversity, with or without nitrogen inputs – and quantified establishment, biomass yield, and biomass composition. In one experiment (‘agronomic trial’), we compared three switchgrass cultivars in monoculture to a switchgrass cultivar mixture and three different species mixtures, with or without N fertilization. In another experiment (‘diversity gradient’), we varied diversity levels in switchgrass and big bluestem (1, 2, 4, or 6 cultivars per plot), with one or two species per plot. In both experiments, cultivar mixtures produced yields equivalent to or greater than the best cultivars. In the agronomic trial, the three switchgrass mixture showed the highest production overall, though not significantly different than best cultivar monoculture. In the diversity gradient, genotypic mixtures had one‐third higher biomass production than the average monoculture, and none of the monocultures were significantly higher yielding than the average mixture. Year‐to‐year variation in yields was lowest in the three‐cultivar switchgrass mixtures and Cave‐In‐Rock (the southern Illinois cultivar) and also reduced in the mixture of switchgrass and big bluestem relative to the species monocultures. The effects of genotypic diversity on biomass composition were modest relative to the differences among species and genotypes. Our findings suggest that local genotypes can be included in biomass cropping systems without compromising yields and that genotypic mixtures could help provide high, stable yields of high‐quality biomass feedstocks.     

Population source affects competitive response and effect in a C4 grass (Panicum virgatum)

Grassland restoration success depends on the development of plant communities that accord with restoration goals. Intraspecific variation in competitiveness may affect community development. For some grassland species, germplasm can be obtained from sources ranging from wild collections to selectively bred cultivars. The extent to which population source affects competitive outcomes in restoration projects is unclear. We addressed this knowledge gap in a glasshouse experiment comparing competitive response and effect among three sources of switchgrass (Panicum virgatum) that are available for restoration: selectively bred cultivars, commercial ecotypes (commercially produced but not deliberately selected), and wild collections. Two strains per source type were grown with four associates chosen to encompass varied functional groups: conspecifics, Bromus inermis, Cirsium arvense, and Solanum ptycanthum. Switchgrass competitive response was evaluated for survival, height, biomass, and shoot:root biomass ratio; competitive effect was assessed as associate survival, height, biomass, and shoot:root ratio. Competitive responses of cultivars and commercial ecotypes were broadly similar, although cultivar biomass exceeded both that of ecotypes and wild collections, and ecotypes had the highest shoot:root ratio. Wild collections were most negatively affected by competition. The shoot:root ratios of all sources were highest when grown with S. ptycanthum, indicating that competitive responses were plastic; plasticity in fitness‐related traits can contribute to persistence in variable environments. Cultivars exerted negative effects on B. inermis. Secondary analyses indicated that all switchgrass sources were most inhibited by the annual S. ptycanthum. To summarize, population source affected multiple aspects of switchgrass competitive ability, when grown against functionally varied associates.     

Grass Invasion into Switchgrass Managed for Biomass Energy

Switchgrass (Panicum virgatum) is a C₄ perennial grass and is the model herbaceous perennial bioenergy feedstock. Although it is indigenous to North American grasslands east of the Rocky Mountains and has been planted for forage and conservation purposes for more than 75 years, there is concern that switchgrass grown as a biofuel crop could become invasive. Our objective is to report on the invasion of C₄ and C₃ grasses into the stands of two switchgrass cultivars following 10 years of management for biomass energy under different N and harvest management regimes in eastern Nebraska. Switchgrass stands were invaded by big bluestem (Andropogon gerardii), smooth bromegrass (Bromus inermis), and other grasses during the 10 years. The greatest invasion by grasses occurred in plots to which 0 N had been applied and with harvests at anthesis. In general, less grass encroachment occurred in plots receiving at least 60 kg of N ha^?1 or in plots harvested after frost. There were differences among cultivars with Cave-in-Rock being more resistant to invasion than Trailblazer. There was no observable evidence of switchgrass from this study invading into border areas or adjacent fields after 10 years of management for biomass energy. Results indicate that switchgrass is more likely to be invaded by other grasses than to encroach into native prairies or perennial grasslands seeded on marginally productive cropland in the western Corn Belt of the USA.     

Improved Feedstock Option or Invasive Risk? Comparing Establishment and Productivity of Fertile <Emphasis Type="Italic">Miscanthus × giganteus</Emphasis> to <Emphasis Type="Italic">Miscanthus sinensis</Emphasis>

The perennial grass genus Miscanthus has great promise as biomass feedstock, but there are concerns about potential invasion outside production fields. While the sterile hybrid Miscanthus × giganteus is currently one of the leading feedstock options due to its low invasive potential, fertile varieties are being developed to reduce establishment costs, and their invasive risks need to be further assessed. We performed seed addition experiments in Ohio and Iowa, USA to examine the establishment, flowering, persistence, and shoot biomass per plot of a fertile M. × giganteus biotype (‘PowerCane’) and two Miscanthus sinensis biotypes, one feral, and one ornamental. Seeds were added to small, replicated plots in each of the 2 years under two seeding densities and two competition treatments, and plots were monitored for 2–3 years. The ‘PowerCane’ biotype established better, survived better, and produced greater amounts of biomass per plot than both M. sinensis biotypes. All three biotypes flowered by the second or third year after establishment, with inflorescences more numerous in ‘PowerCane’ and the Ornamental M. sinensis biotypes. Effects of seeding density and competition on these patterns were minor in most cases. Our research suggests that ‘PowerCane’ exhibits many traits shared by both biomass crops and invasive species: multi-year persistence, high biomass potential, and fertility. We suggest that the benefits of a seeded M. × giganteus should be carefully weighed against its increased invasive risk prior to deployment across the landscape.     

Accelerating the Switchgrass (Panicum virgatum L.) Breeding Cycle Using Genomic Selection Approaches

Switchgrass (Panicum virgatum L.) is a perennial grass undergoing development as a biofuel feedstock. One of the most important factors hindering breeding efforts in this species is the need for accurate measurement of biomass yield on a per-hectare basis. Genomic selection on simple-to-measure traits that approximate biomass yield has the potential to significantly speed up the breeding cycle. Recent advances in switchgrass genomic and phenotypic resources are now making it possible to evaluate the potential of genomic selection of such traits. We leveraged these resources to study the ability of three widely-used genomic selection models to predict phenotypic values of morphological and biomass quality traits in an association panel consisting of predominantly northern adapted upland germplasm. High prediction accuracies were obtained for most of the traits, with standability having the highest ten-fold cross validation prediction accuracy (0.52). Moreover, the morphological traits generally had higher prediction accuracies than the biomass quality traits. Nevertheless, our results suggest that the quality of current genomic and phenotypic resources available for switchgrass is sufficiently high for genomic selection to significantly impact breeding efforts for biomass yield.     

Production of Autopolyploid Lowland Switchgrass Lines Through In Vitro Chromosome Doubling

Switchgrass is considered one of the most promising energy crops. However, breeding of elite switchgrass cultivars is required to meet the challenges of large scale and sustainable biomass production. As a native perennial adapted to North America, switchgrass has lowland and upland ecotypes, where most lowland ecotypes are tetraploid (2n?=?4x?=?36), and most upland ecotypes are predominantly octoploid (2n?=?8x?=?72). Hybridization between lowland and upland switchgrass plants could identify new cultivars with heterosis. However, crossing between tetraploid and octoploid switchgrass is rare in nature. Therefore, in order to break down the cross incompatibility barrier between tetraploid lowland and octoploid upland switchgrass lines, we developed autoployploid switchgrass lines from an anueploid lowland cv. Alamo. In this study, colchicine was used in liquid and solid mediums to chemically induce chromosome doubling in embryogenic calli derived from cv. Alamo. Thirteen autopolyploid switchgrass lines were regenerated from seedlings and identified using flow cytometry. The autoplyploid switchgrass plants exhibited increased stomata aperture and stem size in comparison with the cv. Alamo. The most autooplyploid plants were regenerated from switchgrass calli that were treated with 0.04 % colchicine in liquid medium for 13 days. One autopolyploid switchgrass line, VT8-1, was successfully crossed to the octoploid upland cv. Blackwell. The autoployploid and the derived inter-ecotype hybrids were confirmed by in situ hybridization and molecular marker analysis. Therefore, the results of this study show that an autopolyploid, generated by chemically induced chromosome doubling of lowland cv. Alamo, is cross compatible with upland octoploid switchgrass cultivars. The outcome of this study may have significant applications in switchgrass hybrid breeding.     

Using satellite vegetation and compound topographic indices to map highly erodible cropland buffers for cellulosic biofuel crop developments in eastern Nebraska,USA

Cultivating annual row crops in high topographic relief waterway buffers has negative environmental effects and can be environmentally unsustainable. Growing perennial grasses such as switchgrass (Panicum virgatum L.) for biomass (e.g., cellulosic biofuel feedstocks) instead of annual row crops in these high relief waterway buffers can improve local environmental conditions (e.g., reduce soil erosion and improve water quality through lower use of fertilizers and pesticides) and ecosystem services (e.g., minimize drought and flood impacts on production; improve wildlife habitat, plant vigor, and nitrogen retention due to post-senescence harvest for cellulosic biofuels; and serve as carbon sinks). The main objectives of this study are to: (1) identify cropland areas with high topographic relief (high runoff potentials) and high switchgrass productivity potential in eastern Nebraska that may be suitable for growing switchgrass, and (2) estimate the total switchgrass production gain from the potential biofuel areas. Results indicate that about 140,000 hectares of waterway buffers in eastern Nebraska are suitable for switchgrass development and the total annual estimated switchgrass biomass production for these suitable areas is approximately 1.2 million metric tons. The resulting map delineates high topographic relief croplands and provides useful information to land managers and biofuel plant investors to make optimal land use decisions regarding biofuel crop development and ecosystem service optimization in eastern Nebraska.     

Genetic Structure of Remnant Populations and Cultivars of Switchgrass (Panicum virgatum) in the Context of Prairie Conservation and Restoration

Switchgrass (Panicum virgatum L.) is a dominant, perennial C₄ grass of North American tallgrass prairies with cultivars that are widely used in grassland restoration, pastures, and landscaping. However, these cultivars may be genetically dissimilar to small, remnant populations, raising concerns about altered genetic composition of native populations through gene flow. To address this issue on a local scale in Ohio and Illinois, we used microsatellite markers to characterize genetic diversity and differentiation of 10 remnant prairie populations (5 in each state) and 8 common cultivars. The bulk of genetic variation was found to reside within rather than among wild populations, consistent with the outcrossing breeding system of switchgrass. Genetic diversity was similar among the remnant populations despite large differences in area (approximately 2–2,590 ha), highlighting the importance of small native populations as reservoirs of variation and potential seed sources for prairie restoration. Cultivars generally had similar levels of variation to the wild populations, but we found clear genetic dissimilarity between wild and cultivated gene pools (especially for Kanlow, but also Trailblazer, Blackwell, Dacotah, Summer, and Sunburst cultivars). This suggests that using cultivars in local prairie restoration efforts may alter the genetic composition of wild populations. Whether such changes are deemed as negative depends on the cultivar under consideration and specific conservation goals for preserving native switchgrass populations. Patterns of genetic variation in remnant prairie populations and potential cultivar sources can be used to develop guidelines for restoration as well as future planting of cultivars for biofuels.     

Adaptability evaluation of switchgrass (Panicum virgatum L.) cultivars on the Loess Plateau of China

In the study, the growth traits, photosynthesis and morphology characteristics of several cultivars of switchgrass (Panicum virgatum L.) have been assessed the yield potential and adaptability in diverse environments (Yangling, Dingbian of Shaanxi province, Guyuan of Ningxia) on the Loess Plateau of China. Alamo was the best adapted switchgrass cultivar for biomass production in Yangling with dry matter (DM) yields of 44.22 t/ha; Illinois USA and Cave-in-Rock grown at Guyuan had DM yield of 10.59 t/ha and 9.36 t/ha, respectively. Similarly, Cave-in-Rock in Dingbian performed better than others except the lowland cultivars (Alamo and Kanlow), which could not overcome cold stress at Guyuan and Dingbian. Moreover, Cave-in-Rock and Nebraska 28 has the highest photosynthesis rate which reflects its high productivity. Nebraska 28 and Pathfinder shown strong drought tolerance due to their higher WUE. It appears that the upland cultivars with high ploidy (e.g. 8n) would have better establishment than lowland varieties there. Optimal mown management seems to enhance the growth and productivity of switchgrass. Morphological characteristics were further studied using light-and scanning electron microscopy (SEM). Silica particles, vacuole size and other traits in switchgrass tissues (stem, leaf and root), as well as trichomes (leaf) showed that Cave-in-Rock and Pathfinder had larger stoma area, up to 824.4 μm² and 770.1 μm², respectively. Silica particle length was the longest in Pathfinder and shortest in Cave-in-Rock. There was a highest density of silica particles in cv. Forestberg, and lowest in Cave-in-Rock and Pathfinder. The morphological characters seemed to be associated with their ploidy levels and the arid habitat from which they were selected. Therefore, if switchgrass is to be introduced and extended on the Loess Plateau of China, Cave-in-Rock and other upland cultivars with a high chromosome ploidy might be optimal choices for biomass plants.     

北京地区14份柳枝稷生物量及分配差异研究

采用14份柳枝稷开展盆栽试验,研究了在北京地区条件下其生物量差异及分配规律。结果表明,低地型柳枝稷Kanlow生物量最高,其茎秆、地上部和整株生物量分别达到175.48 g/株、299.18 g/株和447.66 g/株,而高地型柳枝稷Nebraska生物量最低,其茎秆、地上部和整株生物量分别为29.86 g/株、58.08 g/株和140.51 g/株。就柳枝稷整株植株而言,Kanlow地上部生物量分配比例最高,达到63.13%,S2最低,为40.55%,Kanlow地上部营养器官生物量分配比例最高,达到48.67%,Nebraska最低,为31.88%。就柳枝稷地上部而言,Alamo、Kanlow和Trailblazer茎秆生物量分配比例及茎叶比均较高,分别为35.91%和2.75,37.09%和2.56,34.39%和2.48。起源纬度显著影响了柳枝稷的生物量及其分配,就柳枝稷整株植株而言,起源纬度与柳枝稷生物量显著负相关,与地下部生物量分配比例显著正相关,与地上部、种子和茎生物量分配比例显著负相关。就柳枝稷地上部而言,起源纬度与茎生物量分配比例及茎叶比显著负相关,与叶和鞘生物量分配比例显著正相关。生物量的差异及其分配规律反映出柳枝稷对生态环境长期适应的生殖与生长策略。本研究为柳枝稷遗传资源引种和品种选育提供了依据。     

The Feasibility of Producing Adequate Feedstock for Year-Round Cellulosic Ethanol Production in an Intensive Agricultural Fuelshed

To date, cellulosic ethanol production has not been commercialized in the United States. However, government mandates aimed at increasing second-generation biofuel production could spur exploratory development in the cellulosic ethanol industry. We conducted an in-depth analysis of the fuelshed surrounding a starch-based ethanol plant near York, Nebraska that has the potential for cellulosic ethanol production. To assess the feasibility of supplying adequate biomass for year-round cellulosic ethanol production from residual maize (Zea mays) stover and bioenergy switchgrass (Panicum virgatum) within a 40-km road network service area of the existing ethanol plant, we identified ～14,000 ha of marginally productive cropland within the service area suitable for conversion from annual rowcrops to switchgrass and ～132,000 ha of maize-enrolled cropland from which maize stover could be collected. Annual maize stover and switchgrass biomass supplies within the 40-km service area could range between 429,000 and 752,000 metric tons (mT). Approximately 140–250 million liters (l) of cellulosic ethanol could be produced, rivaling the current 208 million l annual starch-based ethanol production capacity of the plant. We conclude that sufficient quantities of biomass could be produced from maize stover and switchgrass near the plant to support year-round cellulosic ethanol production at current feedstock yields, sustainable removal rates and bioconversion efficiencies. Modifying existing starch-based ethanol plants in intensive agricultural fuelsheds could increase ethanol output, return marginally productive cropland to perennial vegetation, and remove maize stover from productive cropland to meet feedstock demand.     

Linkage Maps of Lowland and Upland Tetraploid Switchgrass Ecotypes

Switchgrass (Panicum virgatum L.) is a native perennial warm season (C₄) grass that has been identified as a promising species for bioenergy research and production. Consequently, biomass yield and feedstock quality improvements are high priorities for switchgrass research. The objective of this study was to develop a switchgrass genetic linkage map using a full-sib pseudo-testcross mapping population derived from a cross between two heterozygous genotypes selected from the lowland cultivar ‘Alamo’ (AP13) and the upland cultivar ‘Summer’ (VS16). The female parent (AP13) map consists of 515 loci in 18 linkage groups (LGs) and spans 1,733 cM. The male parent (VS16) map arranges 363 loci in 17 LGs and spans 1,508 cM. No obvious cause for the lack of one LG in VS16 could be identified. Comparative analyses between the AP13 and VS16 maps showed that the two major ecotypic classes of switchgrass have highly colinear maps with similar recombination rates, suggesting that chromosomal exchange between the two ecotypes should be able to occur freely. The AP13 and VS16 maps are also highly similar with respect to marker orders and recombination levels to previously published switchgrass maps. The genetic maps will be used to identify quantitative trait loci associated with biomass and quality traits. The AP13 genotype was used for the whole genome-sequencing project and the map will thus also provide a tool for the anchoring of the switchgrass genome assembly.     

Switchgrass (Panicum virgatum L.) Genotypes Differ between Coastal Sites and Inland Road Corridors in the Northeastern US

Switchgrass (Panicum virgatum L.) is a North American grass that exhibits vast genetic diversity across its geographic range. In the Northeastern US, local switchgrass populations were restricted to a narrow coastal zone before European settlement, but current populations inhabit inland road verges raising questions about their origin and genetics. These questions are important because switchgrass lines with novel traits are being cultivated as a biofuel feedstock, and gene flow could impact the genetic integrity and distribution of local populations. This study was designed to determine if: 1) switchgrass plants collected in the Long Island Sound Coastal Lowland coastal Level IV ecoregion represented local populations, and 2) switchgrass plants collected from road verges in the adjacent inland regions were most closely related to local coastal populations or switchgrass from other geographic regions. The study used 18 microsatellite markers to infer the genetic relationships between 122 collected switchgrass plants and a reference dataset consisting of 28 cultivars representing ecotypes, ploidy levels, and lineages from North America. Results showed that 84% of 88 plants collected in the coastal plants were most closely aligned with the Lowland tetraploid genetic pool. Among this group, 61 coastal plants were similar to, but distinct from, all Lowland tetraploid cultivars in the reference dataset leading to the designation of a genetic sub-population called the Southern New England Lowland Tetraploids. In contrast, 67% of 34 plants collected in road verges in the inland ecoregions were most similar to two Upland octoploid cultivars; only 24% of roadside plants were Lowland tetraploid. These results suggest that cryptic, non-local genotypes exist in road verges and that gene flow from biofuels plantations could contribute to further changes in switchgrass population genetics in the Northeast.     

Infestation Rates and Tiller Morphology Effects by the Switchgrass Moth on Six Cultivars of Switchgrass

Switchgrass (Panicum virgatum L.) is a potential biomass crop for native species-based biofuel systems in North America. A recently identified pest of switchgrass, the switchgrass moth, Blastobasis repartella (Dietz) (Lepidoptera: Coleophoridae), feeds in the basal above-ground internodes and below-ground in the proaxis and rhizomes, causing premature tiller and rhizome loss. Our goal was to determine genetic and temporal variation among six upland cultivars for frequency of tiller infestation by larvae of the switchgrass moth in mature stands in the northern Great Plains and if variation in biomass production was associated with variation in frequency of infestation. Data were collected in 2011 and 2012 for tiller density, biomass, frequency of infestation, number of leaves per healthy and infested tiller, and weights of healthy and infested tillers. Differences were found among cultivars for tiller density, biomass yield, and numbers of leaves per healthy and infested tillers. ‘Summer’, ‘Sunburst’, ‘Pathfinder’, and ‘Cave-In-Rock’ were the highest yielding cultivars. Mean frequency of infestation was different between 2011 (6.7 %) and 2012 (9.6 %). Infested tillers had one less collared leaf than healthy tillers. The weights of healthy tillers were ca. 3× those of infested tillers in both years, suggesting an impact on biomass accumulation and economic value. Levels of infestation were similar for all six cultivars, indicating no feeding preference by the switchgrass moth larva among genetically diverse cultivars of switchgrass. Regression of biomass yield on frequency of infestation showed negative linear relationships for ‘Carthage’ and ‘Kentucky 1625’.