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Development of perennial biomass cropping systems is focused on maximizing biomass yield with minimum inputs, particularly nitrogen (N) fertilizer. Historical breeding efforts have focused on increasing biomass yield but have ignored N-use efficiency. The purpose of this study was to quantify the increased N demand associated with realized gains in biomass yield from big bluestem (Andropogon gerardii Vitman) and switchgrass (Panicum virgatum L.) breeding programs. Nitrogen demand was highly variable across locations and years, ranging from − 1.7 to + 6.8 kg N Mg−1 DM, with an average of 2.2 kg N Mg−1 DM. Increases in N demand were closely associated with realized gains in biomass yield and were observed for all types of switchgrass (upland, lowland, and hybrid) as well as for big bluestem. Attenuation of these responses will require alternative breeding schemes that are focused on evaluation of switchgrass genotypes and progeny under low-N conditions and include a high-throughput tissue N analysis as a component of future selection criteria, designed to develop new cultivars with high biomass yield and low tissue N.

Prairie cordgrass (Spartina pectinata, Link.) has been evaluated for its biomass potential because of its high yield, relatively low nutrient demand, and diverse geographical adaptation. Our objectives were to determine (1) biomass production potential of prairie cordgrass in South Dakota and Kansas under varying nitrogen levels, (2) the effect of N on prairie cordgrass yield components (tillers m−2 and tiller mass), and (3) the effect of N on yield and N concentration of belowground biomass. Older stands of Red River prairie cordgrass (RR-PCG) in South Dakota and Atkins prairie cordgrass (AT-PCG) in Kansas were fertilized with 0, 56, 112 and 168 kg N ha−1 from 2008 to 2011 in South Dakota and in 2009 and 2010 in Kansas. Experimental design at all locations was a 4 × 4 Latin square. Prairie cordgrass was harvested around a killing frost in October and early November. Biomass production ranged from 5.50 to 13.69 Mg ha−1 in South Dakota and 5.33 to 12.51 Mg ha−1 in Kansas. Prairie cordgrass yield did not increase significantly with N application at any location or year. Across years, tiller density ranged from 536 to 934 tillers m−2 for RR-PCG in South Dakota and from 234 to 315 tillers m−2 for AT-PCG in Kansas. Neither tiller density or tiller mass was affected by N rate at any location in any year. Belowground biomass production to a depth of 25 cm was equal to or greater than aboveground biomass. However, it was not affected by N rate in all locations by any year. Understanding prairie cordgrass nitrogen-use dynamics to improve biomass and nutrient management will be essential for future investigations. Findings of this study are important to support the notion that prairie cordgrass biomass production in two different environments can be achieved with minimal N inputs.

The salt-tolerant capability of the candidate bioenergy crop prairie cordgrass greatly surpasses that of previously characterized prairie grass species and most other plants. To understand the mechanism of inherited salt tolerance, we compared phenotypic and genetic qualities in half-sib families of prairie cordgrass after salt treatment. Each family was treated with a 400 mM NaCl solution or a water control and then measured for various health phenotypes. Phenotypes associated with salt tolerance were shown to be moderately heritable between parent and offspring. RNA-seq analysis revealed differential regulation in unique pathways including metabolism, signaling, photosynthesis, and the circadian rhythm. The studies herein suggest that alternative regulation of the photosynthetic pathway could confer increased salt resistance in halophytes and can be monitored phenotypically or genetically in breeding programs. The improvement of salt-tolerant traits in prairie cordgrass would increase its potential to be grown as a bioenergy crop on lands that are not suitable for the growth of food crops.

Prairie cordgrass (Spartina pectinata Link) is a productive warm-season, C4 perennial grass native to most of North America having tolerance to wet, cold, and saline growing conditions. Excellent stress tolerance, along with high biomass yields, makes prairie cordgrass a good candidate as a dedicated energy crop on marginal land. However, there is little information available on genetic variation, including yield potential, of native populations in the USA. The objectives of this study were to evaluate biomass yield and to identify the nature and extent of genetic variation in natural populations of prairie cordgrass by comparing endemic strains collected throughout the USA. Forty-two prairie cordgrass populations were collected from prairie-remnant sites in 13 states and evaluated at the University of Illinois in Urbana, IL. The 4-year field study of prairie cordgrass revealed extensive variations in biomass yield and phenotypic traits associated with biomass yield among these populations. Strong correlations were observed between the phenotypic values and origins of the populations. Path coefficient analysis indicated that tiller mass, tiller density, heading date, plant height, and phytomer number positively affected biomass yield directly or indirectly. However, the phenotypic traits including biomass yield showed significant variation among years except for phytomer number and heading date. With the extensive genetic variability and high biomass yield potential demonstrated in this experiment, prairie cordgrass could become a highly productive bioenergy crop by developing a well-planned breeding program.

Switchgrass (Panicum virgatum L.) is considered to be a highly promising bioenergy crop. However, little is known about insect pests that impact its utilization for this purpose. The switchgrass gall midge [Chilophaga virgati Gagne (Diptera: Cecidomyiidae)], which was first discovered in 2008 at Brookings, SD, USA, is shown to have a negative impact on biomass and seed yields of switchgrass. Our objectives were to increase knowledge of the biology of the midge by describing its life stages and any parasitoids that have biological control potential. Data collections were made during May to December in 2011 and April to late autumn in 2012. The gall midge adult is active from early June to late July. This insect overwinters as a late instar larva, usually in large aggregations, enclosed in the sheath of the flag leaf of dry tillers. The mean number of larvae was 31, with a range of 6 to 85 per tiller. Infested tillers m−2 varied among three phenologically distinct cultivars. The late flowering cultivar ‘Cave-In-Rock’ was more heavily infested (>2×) than the early flowering ‘Dacotah’. A newly discovered parasitoid, Platygaster chilophagae Buhl (Hymenoptera: Platygastridae) and a species of Quadrastichus sp. (Hymenoptera: Eulophidae) were reared from gall midge larvae. These results will be valuable to entomologists, switchgrass breeders, and agronomists as a guide to the occurrence and activities of the gall midge.

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’.

High yielding, native warm-season grasses could be used as renewable bioenergy feedstocks. The objectives of this study were to determine the effect of warm season grass monocultures and mixtures on yield and chemical characteristics of harvested biomass and to evaluate the effect of initial seeding mixture on botanical composition over time. Switchgrass (Panicum virgatum L.), indiangrass [Sorghastrum nutans (L.) Nash], and big bluestem (Andropogon gerardii Vitman) were planted as monocultures and in all possible two- and three-way mixtures at three USA locations (Brookings and Pierre, SD and Morris, MN) during May 2002. Biomass at each location was harvested after a killing frost once annually from 2003 to 2005. Total biomass yield significantly increased with year at all locations. Switchgrass monocultures or mixtures containing switchgrass generally out-yielded big bluestem or indiangrass in monocultures or the binary mixture. Cellulose and hemicellulose concentrations were higher in 2004 and 2005 compared with 2003. Switchgrass or mixtures containing switchgrass tended to have less cellulose than either big bluestem or indiangrass. Results were more variable for total N, lignin, and ash. Switchgrass was the dominant component of all mixtures in which it was present while big bluestem was dominant when mixed with indiangrass. Indiangrass was maintained only in monocultures and declined over years when grown in mixtures at all locations. Our results indicated if biomass yield in the northern Great Plains is a primary objective, switchgrass should be a component of binary or tertiary mixtures that also contain big bluestem and/or indiangrass.

A new species of gall midge, Chilophaga virgati Gagne (Diptera: Cecidomyiidae), collected from tillers of switchgrass at Brookings, South Dakota (44.31134° N, 96.78374° W) is described here. Plant morphological symptoms of infestation and frequency of tillers infested are also provided. Full-grown larvae of C. virgati were found inside the sheath of the flag leaf of reproductive tillers of clonally replicated spaced plants of a selected southern upland population of switchgrass during October 2008 and 2009. Infested tillers were shorter and lighter than normal tillers and had panicles that were partially encased in the sheath of the flag leaf due to reduced elongation of the peduncle as a result of the feeding of larvae of C. virgati at the proximal end of the panicle and in the intercalary meristem area of the peduncle. Variation was found among 10 genotypes for percentage of tillers infested by C. virgati, with a range from 7.2% to 21.8%. No difference was found between years for infestation rate (12.7% in 2008 and 14.3% in 2009). The mass of infested tillers was 35% that of normal tillers, and infested tillers produced no appreciable amount of viable seeds. Results of this research revealed that C. virgati had direct negative impacts on biomass and seed production in spaced plant nurseries of switchgrass. C. virgati was also observed in seeded swards of northern upland switchgrass cultivars, but its impact in seeded swards has not yet been determined.