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Vegetative filter strip characteristics such as perenniality drive hydrology and subsequent ecosystem services. However, the extent and the potential for forage–biomass crops to improve water quality, provide fodder, and optimize nutrient cycling in multifunctional systems is unknown. We evaluated (a) how species, perenniality, and plant community composition are linked to water quality; and (b) the multiuse forage–biomass potential of filter strips. Whole plots were species [eastern gamagrass (Tripsacum dactyloides), Kernza [or intermediate wheatgrass (Thinopyrum intermedium)], silphium (Silphium integrifolium), switchgrass (Panicum virgatum), and winter wheat (Triticum aestivum)], with split‐plots receiving 0 or 5.6 Mg ha−1 broiler litter. Rainfall simulations were conducted at 5 cm h−1 (until 30 min of continuous runoff) in summer and fall of 2019 and 2021 with dual forage and biomass harvests occurring 2019–2021. Kernza and silphium had the lowest biomass regrowth after forage harvests relative to native grasses, suggesting they would not be ideal multifunctional forage–bioenergy crops. Among all soil–plant–water variables, canonical correlations indicate poultry litter (.97), and soil phosphorus saturation (.77) were the most influential variables for water quality. Water quality score, FWQ, which is inversely related to runoff water quality, was lowest for switchgrass (0.03) and greatest (P ≥.05) for eastern gamagrass and wheat (1.77 and 3.33, respectively), but not different from Kernza (0.98) and silphium (0.31). Therefore, switchgrass resulted in the best water quality scores and highest forage–biomass yields, with Kernza and silphium also showing promise for reducing sediment and nutrient loads following poultry litter applications in multifunctional filter strip systems. Core Ideas: Filter strip characteristics drive surface hydrology and subsequent ecosystem services. Greatest multiuse (forage–biomass filter strip) yields occurred for switchgrass. Poultry litter applications and soil P saturation were most correlated with water quality. Perennial crops (excluding eastern gamagrass) improved water quality. Switchgrass had the highest water quality and biomass yields, indicating greatest multiuse filter strip potential. [ABSTRACT FROM AUTHOR]

Switchgrass (Panicum virgatum L.) breeders use spaced‐seedling plots for evaluations of biomass yield, but prior studies are ambiguous about the relationship between performance in spaced plots and commercial seeded sward performance. This study used a split‐plot incomplete block design to evaluate 52 half‐sib switchgrass families across two years to determine the correlations among four different plot types (including seeded swards) and four individual plant traits. Plots (1.62 m2) that contained 3, 6, and 18 plants had mean yields of 5.92, 8.04, and 11.06 Mg ha–1, respectively, while seeded‐sward plots had a mean of 5.37 Mg ha–1. In a mixed‐model analysis including family‐, year‐, and plot‐type interactions with a spatial‐spline correction, the largest proportion of family variance was accounted for by the main family effect (48%), while the plot type‐by‐family effect was only 17% of family variance. These results indicate that spaced‐plant plots are reasonable surrogates for biomass performance in sward conditions. Yield reliability was 0.50 across all plot types with a mean of 0.46 for individual plot types. Surrogates for sward yield varied due to genetic background of the families. Yield of families derived from the Liberty cultivar (n = 32) had genetic correlations with winter survivorship scores (0.66). Diverse lowland ecotype families (n = 20) had genetic correlations with plant height and heading date. This study highlighted a major difference in performance among the plot types, specifically that seeded swards have depressed yield due to high plant density. This should encourage further research for the mechanism behind this difference in performance. [ABSTRACT FROM AUTHOR]

Heterosis plays an important role in switchgrass (Panicum virgatum L.) breeding. To identify superior clones for hybrid development through seasonal single cut, 10 crosses derived from 'Alamo' × 'Kanlow' and parents were evaluated. The experiment was planted in 2018 using a randomized complete block design with two replications at two locations in Tennessee: the East Tennessee Research and Education Center (ETREC), Knoxville, and the Plateau Research and Education Center (PREC), Crossville. The crosses and their parents were evaluated for biomass yield, plant height, and clonal mass in the fall of 2019 and 2020. The crosses were significantly different in biomass yield within and across locations (P = .05). Average biomass yield of the crosses ranged from 7.1 to 8.7 Mg ha-1 at ETREC and from 10.0 to 11.8 Mg ha-1 at PREC. The crosses demonstrated an average of 46% mid-parent heterosis (MPH) and 24% high-parent heterosis (HPH) for biomass yield across the two locations. The MPH and HPH were 3 and -1.3% for plant height and 12 and 1% for clonal mass, respectively. Moderate to strong positive association was found between clonal mass scores and biomass yield at individual locations across years and across locations and years (r = 0.37-0.79, P = .05). The association between biomass yield and plant height was inconsistent (r = -0.24 to 0.67, P = .05). The findings of biomass yield heterosis in these crosses suggested the potential of hybrid cultivars for biomass yield improvement in lowland switchgrass. [ABSTRACT FROM AUTHOR]

Switchgrass (Panicum virgatum L.) is a promising candidate species for sustainable biofuel feedstock production on marginal land. Soil salinity is one of the significant factors that limits sustainable agricultural production worldwide including a substantial reduction in biomass yield of switchgrass. This study was designed to assess genetic variation in lowland switchgrass and identify genomic regions contributing to an increased level of salinity tolerance using a subset (550 pseudo F2) of a nested association mapping (NAM) population. Salinity tolerance was evaluated based on salt injury score (SIS) using a 1 to 9 scale (1 = the most tolerant, 9 = the most sensitive) and stress tolerance index (STI) calculated from plant height measurements. Substantial variation among NAMfamilies and genotypes within families was observed (p < .05) for SIS. However, no variation was evident among NAM families and genotypes within families for STI. The switchgrass plant accessions EG 1104-1, and EG 1104-2 displayed a high level of salinity tolerance based on SIS which can be used as source material for cultivar development. A total of five quantitative trait loci (QTL) associated with SIS were detected by composite interval mapping on four chromosomes 2B, 6B, 7B, and 9B. The phenotypic variation explained by an individual QTL ranged from 1.4 to 6.5%. The additive genetic effects of individual QTL ranged from -0.07 to 0.63. Homologs of five candidate genes were identified, which were reported to be associated with salinity tolerance. [ABSTRACT FROM AUTHOR]

Obtaining good accuracy and reliability of estimated breeding values is essential to increase the efficiency of a plant breeding program. Genetic variation was assessed for categorical (Virc) and binary (Virb) mosaic (caused by Panicum mosaic virus), dry matter (DMY) and predicted ethanol (Etoh) yields, and lignin content (Klason or KL, and acid‐detergent or ADL) in a Summer–Kanlow switchgrass (Panicum virgatum L.) population. Breeding values were predicted with the restricted maximum likelihood–best linear unbiased prediction (REML‐BLUP) approaches using a multivariate phenotypic (PBLUP) and animal (ABLUP) models, integrating a three‐generation pedigree (1,622 half‐sibs) in ABLUP and not in PBLUP. Models were compared in their precision (accuracy and reliability) in assessing genetic parameters and estimating breeding values. The models were similar in most aspects, allocating the highest heritability (hi2) values to DMY (.38 ±.035 vs..41 ±.035), Etoh (.46 ±.031 vs..42 ±.033), and Virc (.43 ±.046 vs..37 ±.047) and the lowest (.17 ±.032 to.30 ±.044) to KL, ADL, and Virb. Genetic correlations were always larger than residual and phenotypic correlations. Intermediate or strong additive genetic control suggest that selecting for high‐biomass genotypes will slightly increase lignin content and simultaneously impart mosaic tolerance. Mitigating an increase in lignin content will require including Etoh in a selection index based on its much stronger negative correlation (rG = −.63) with lignin. In this population, accuracy values ranged from.06 to.94 (PBLUP) and from.26 to.92 (ABLUP) and corresponding reliability ranged from.004 to.89 and from.07 to.87. However, ABLUP improved average reliability of DMY and Etoh by 11% and of other traits by 4–5% over the PBLUP model. The ABLUP was a better model over PBLUP, which is a valid analysis in the absence of a pedigree. Core Ideas: Across‐generation BLUP analysis provides greater accuracy than one‐generation analysis.An across‐generation animal model is a better model than a phenotypic analysis.Decreasing lignin content by breeding in switchgrass will help increase ethanol yield.Genotypes with higher lignin content tend to have greater disease tolerance and resistance. [ABSTRACT FROM AUTHOR]

Manganese is an essential nutrient and plays key roles in photosynthetic processes, including in NAD‐malic enzyme (NAD‐ME)‐type C4 plants as an activator of NAD‐ME. However, little is known about the Mn requirements of switchgrass (Panicum virgatum L.). To study Mn requirements for optimum growth and biomass production, a lowland ('Alamo') and an upland ('Cave‐in‐Rock') switchgrass ecotype were grown with either washed sand, vermiculite, or perlite and fertilized with nutrient solutions ranging in [Mn] from 0 to 200 μM. In the perlite experiment, pearl millet [Pennisetum glaucum (L.) R. Br. 'KGraze'] was also grown. Shoot [Mn] was highly responsive to increasing Mn in the nutrient solution. When grown in washed sand and vermiculite, tissue [Mn] remained above those normally considered deficient, even in the 0 μM Mn treatment, and no Mn treatment effects on biomass production were found. In perlite, end‐of‐season shoot [Mn] were <5 mg kg−1 in all entries when no Mn was supplied, and a decrease in biomass production compared with 10–25 μM Mn treatments was observed for Alamo and KGraze, but not for Cave‐in‐Rock. Relative chlorophyll contents of switchgrass were lower in the 0 μM Mn treatment than in other treatments late in the season, but in KGraze, they were low early in the season and increased throughout the season, resulting in less pronounced (but still significant) differences at late stages. Overall, results indicated that switchgrass and pearl millet respond differently to low Mn availability and that even low levels of shoot tissue [Mn] allow switchgrass to maintain biomass production. [ABSTRACT FROM AUTHOR]

The quality of predicted plant‐, soil‐, and animal‐response values from near‐infrared (NIR) reflectance spectra depends on the ability to generate appropriate NIR models. The first step in the development of NIR models is collection of spectral data. Limited work, however, has been reported that compares NIR models for prediction of forage nutritive value when the spectra are obtained from devices with different spectral ranges and resolutions. The objectives of this study were to (a) develop and evaluate NIR spectroscopy models using a benchtop‐type (FOSS) and two handheld NIR devices (microPHAZIR and DLP NIRscan Nano EVM) to predict crude protein (CP), acid detergent fiber (ADF), amylase and sodium sulfite‐treated neutral detergent fiber (aNDF), and in vitro true dry matter digestibility (IVTD) of dried ground forage grass samples and (b) compare predictions among the three NIR devices. Switchgrass (Panicum virgatum L.) and bermudagrass [Cynodon dactylon (L.) Pers] hay samples were scanned with the NIR devices and analyzed with wet chemistry for development of NIR prediction models. Among devices, the r2 of validation values for aNDF models ranged from.81 to.87; all other r2 values were >.86 and as high as.98 with standard error of prediction (SEP; g kg−1) ranging from 8.1 to 11.5 for CP, 19.1 to 23.8 for aNDF, 14.2 to 20.0 for ADF, and 26.8 to 49.9 for IVTD. The FOSS benchtop NIR prediction models consistently had the highest r2 and lowest SEP values; however, the predictive power for both handheld devices was similar to the benchtop‐type device. [ABSTRACT FROM AUTHOR]

Switchgrass (Panicum virgatum L.) has become an important biofuel crop. The experiment was designed to identify differentially expressed genes (DEGs) for flowering time in switchgrass genotypes contrasting in heading and anthesis dates. Phytomers of early‐ (S041) and late‐flowering (B901) parents and early‐ (7071) and late‐flowering (7055) F2 genotypes were collected on two sampling dates of vegetative stages, and transcriptome profiling was completed to identify DEGs involved in flowering time using RNA sequencing. Across two sampling dates, the comparison between S041 and B901 identified six upregulated (TOC1, FKF1, two PHYA, and two PFT1) and five downregulated flowering DEGs (FT, GASA, COP1, and two CHS) in S041, but one upregulated FT and one downregulated GASA in B901. When comparing two F2 genotypes, three DEGs (PFT1 and two FT) were upregulated in 7071, and six DEGs (PRR7, PRR5, PHYB, TOC1, and two CKB4) were upregulated and one DEG (COP1) was downregulated in 7055 genotype. The upregulation of PRR5 and FKF1 and downregulation of GASA and COP1 were found in both early‐flowering genotypes, whereas FKF1, PRR5, PRR7, and PHYB were upregulated and two GASA were downregulated in both late‐flowering genotypes. Across both early‐flowering genotypes, seven upregulated and 12 downregulated transcription factors (TFs) from nine families related to flowering were differentially expressed, whereas eight upregulated and 30 downregulated flowering related TFs from 16 families were differentially expressed across both late‐flowering genotypes. The identification of key genes involved in the flowering pathways could facilitate the development of desirable flowering phenotypes of switchgrass. [ABSTRACT FROM AUTHOR]

Forage species with greater nutritive value have the potential to positively affect animal responses. 'Performer' switchgrass (Panicum virgatum L.) was released because of greater digestibility and lower lignin concentrations as compared to 'Alamo' and 'Cave‐in‐Rock.' However, the relationship between nutritive value, canopy characteristics, and dry matter yield for this species has not yet been established. The goal of this study was to determine in vitro true digestibility (IVTD), crude protein (CP), neutral detergent fiber (NDF), and acid detergent fiber (ADF) as a function of a wide range of defoliation management strategies to aim optimize production of nutritious forage. Treatments were the factorial combination (4 × 4) of defoliation height (DH; clipped to 10, 20, 30, and 40 cm) and defoliation frequency (DF; clipped every 3, 6, 9, and 12 wk). The range of digestibility values was greater due to DF (from 590–779 g kg−1 when averaged across DH treatments) than DH treatments (from 675–692 g kg−1 when averaged across DF treatments). In general, frequent defoliation resulted in greater IVTD and CP but lower yields; however, there were interaction effects of DF × DH for all response variables. With the exception of NDF, all response variables had strong correlations with dry matter yield, canopy height, and leaf/stem ratio. Although there are tradeoffs when managing for productivity and nutritive value, there is a wide range of defoliation management options for 'Performer' switchgrass that provide flexibility in terms of harvesting schedules to optimize productivity and persistence of nutritious forage. [ABSTRACT FROM AUTHOR]

Defoliation management can determine the presence or absence of desirable forage species. Canopy characteristics and light interception are two critical determinants of productivity and can influence weed pressure. The objectives of this study were to determine the effect of the factorial combination of four defoliation heights (clipped to 10, 20, 30, and 40 cm; DH) and four defoliation frequencies (clipped every 3, 6, 9, and 12 wk; DF) on light interception, canopy height, and weed canopy cover and frequency for 'Performer' (Panicum virgatum L.) switchgrass and to relate the abovementioned responses to previously reported productivity measurements. The experiment was conducted for 2 yr (2016 and 2017) at the Central Crops Research Station, Clayton, NC. The 16 treatments were allocated in a randomized complete block design replicated four times. Across years, light interception before harvest ranged from ∼45 to 88%, canopy height ranged from 35 to 97 cm, and weed cover and frequency ranged from 0 to 75 and 0 to 95%, respectively. Greater canopy height was associated with greater light interception and lower weed infestation. Weed infestation occurred mainly for treatments harvested every 3 and 6 wk and defoliated to lower stubble heights; however, there was no impact of DH for DF treatments harvested every 9 and 12 wk. Canopy light interception values of at least 70% obtained in our study were associated with defoliation thresholds previously reported in the literature for sustained yields of 'Performer' switchgrass. Switchgrass canopy light interception values of at least 70% were achieved with canopy heights before harvest of ∼60 cm tall. [ABSTRACT FROM AUTHOR]

Development of switchgrass (Panicum virgatum L.) as a dedicated bioenergy feedstock requires intensive and extensive breeding programs that include careful and thoughtful consideration of appropriate target populations of environments (TPEs). The purpose of this study was to evaluate region (climate), soil quality, and N fertilization level as potential factors influencing the choice of TPE. A total of 45 switchgrass genotypes were evaluated in uniform field studies at six field sites defined as prime or marginal soils in New Jersey, South Dakota, and Wisconsin. Region and soil quality had strong interactions with genotype, but N fertilization had little impact on genetic variation or ranking of genotypes. Lowland genotypes were considerably more sensitive than upland genotypes to interactions with environmental factors, probably due to these field sites being outside of the traditional lowland adaptation zones. Genotype rankings were highly inconsistent across regions and soil types, indicating that breeding programs that target marginal soils should be located on soils that represent the appropriate TPE. Furthermore, interactions across the three regions suggest that breeding programs for the lowland ecotype should be subdivided into different sets of TPEs, which are largely a function of hardiness zone and annual precipitation. Lastly, even with negligible interactions involving N fertilization level, future definitions of TPEs should be based on minimal or no N fertilizer applications to allow breeders to select plants with greater N-use efficiency, N-scavenging ability, and N-recycling efficiency. [ABSTRACT FROM AUTHOR]

Increases in biomass yield of switchgrass (Panicum virgatum L.) have been achieved, but the rate of gain has been slow and would benefit from improved efficiency of selection methods. Dry matter (DM) determinations at the time of harvest are a traditional method to adjust fresh matter yield (FMY) to a DM basis. The purpose of this study was to determine if DM determinations in switchgrass yield evaluations are necessary or unnecessary. Data from 219 trial-years of 11 published experiments were used to evaluate the value of DM adjustment. Heritability for FMY and dry biomass yield (DBY) were similar, and the genetic correlation between these two traits was >0.8 for 96.7% of the trial-years. The direct effect of FMY on DBY was three to four times greater than the direct effect of DM concentration. Because DM determination requires a larger field crew at the time of harvest, the use of FMY as a selection criterion requires significantly less labor than DBY at harvest time. Tripling the number of families evaluated and eliminating the DM step would increase the expected genetic gain for DBY by 17%. However, decreasing the number of replicates per family while eliminating the DM step would undermine the gains in efficiency due to reduced heritability for FMY. Although the risk of using FMY is low, achieving this increase in efficiency requires a serious commitment to evaluating a very large number of replicated families in each generation, an effort that may be beyond the ability and scope of most breeding programs. [ABSTRACT FROM AUTHOR]

Breeding to improve biomass production of switchgrass (Panicum virgatum L.) and big bluestem (Andropogon gerardii Vitman) for conversion to bioenergy began in 1992. The purpose of this study was (i) to develop a platform for uniform regional testing of cultivars and experimental populations for these species, and (ii) to estimate the gains made by breeding during 1992 to 2012. A total of 25 switchgrass populations and 16 big bluestem populations were planted in uniform regional trials at 13 locations in 2012 and 2014. The reference region was USDA Hardiness Zones 3 through 6 in the humid temperate United States. Significant progress toward increased biomass yield was made in big bluestem and within upland-ecotype populations, lowland-ecotype populations, and hybrid-derived populations of switchgrass. Four mechanisms of increasing biomass yield were documented: (i) increased biomass yield per se, (ii) later flowering to extend the growing season, (iii) combined later flowering from the lowland ecotype with survivorship of the upland ecotype in hybrid-derived populations, and (iv) increased survivorship of late-flowering lowland populations in hardiness zones that represent an expansion of their natural adaption zone. Switchgrass exhibited all four mechanisms in one or more improved populations, whereas improved populations of big bluestem were likely influenced by two of the four mechanisms. The uniform testing program was successful at documenting increases in biomass yield, identifying the mechanisms for increased yield, and determining adaptation characteristics and limitations of improved populations. [ABSTRACT FROM AUTHOR]

Switchgrass (Panicum virgatum L.), a native of the North American prairies, has been selected for bioenergy research. With a focus on biomass yield improvement, this study aim (i) to estimate the genetic variation in biomass yield and important agronomic traits in 'Alamo', (ii) to determine correlations between biomass yield and agronomic traits, and (iii) to compare efficiency of phenotypic selection from a sward plot and advanced cycle half-sibs (ACHS) on the basis of space-plant performance. Sixtytwo Alamo half-sib families (AHS) from a 4-yr-old Alamo sward and 20 advanced cycle half-sib families (ACHS) were evaluated in replicated field trials under simulated swards in Knoxville and Crossville, TN. Results showed significant variation (P < 0.05) among AHS for biomass yield, tillering ability, and spring vigor, suggesting the importance of additive genetic variation in these traits. Overall mean biomass yield of AHS was not different from the Alamo control, demonstrating the inefficiency of phenotypic selection from swards. Mean biomass yield of ACHS was 15 and 20% less than that of the control and AHS, respectively. Such results could be attributable to the influence of environment and genotype × environment interaction. However, results showed great potential for biomass yield improvement through selection on the basis of family performance. Using 10% selection intensity, parental control of two, and a narrow-sense heritability estimate of 0.11, gain per cycle selection from half-sib family selection is estimated to be 23%. Spring vigor showed potential use for indirect selection due to its high genetic correlation (rG = 0.75) with biomass yield. However, it is impeded by the low heritability estimate (h2 = 0.34). [ABSTRACT FROM AUTHOR]

Phenological and morphological behaviors under variable temporal and spatial environmental conditions provide essential information for breeding native perennial warm-season grasses for bioenergy and ecosystem goods and services. Among various environmental factors, natural photoperiodic signals can affect both vegetative and reproductive growth of perennial species. In this study, field-collected plants of switchgrass (Panicum virgatum L.) and prairie cordgrass (Spartina pectinata Link) were subjected to ambient photoperiods of either increasing or decreasing daylength during the dormant period of their normal growth cycles in a temperature-controlled greenhouse. Upland switchgrass reacted to a short-day treatment (decreasing or increasing daylength <12 h) with a less synchronized dormancy-breaking pattern than prairie cordgrass. Prairie cordgrass showed a strict daylength overriding dormancybreaking pattern. However, phenological and morphological traits observed during the growing season through reproductive development and senescence indicated that the capacity to reach sexual maturity for both species was not greatly affected by subjection to noninductive photoperiod immediately after breaking dormancy. Overall, our results indicated that switchgrass coped with unfamiliar natural photoperiod conditions better than prairie cordgrass in terms of vegetative and reproductive growth. [ABSTRACT FROM AUTHOR]

Biomass yield improvement of switchgrass (Panicum virgatum L.) is critical for its use as a viable bioenergy feedstock. Population improvement through accumulation of favorable genes and exploitation of heterosis are two ways to improve biomass yield. The objective of this study was to assess biomass yield heterosis in biparental crosses between genotypes of low-land switchgrass. Forty-four genotypic crosses between two predominant lowland populations 'Alamo' and 'Kanlow', along with nine crosses among genotypes of other lowland germplasm, were evaluated in Knoxville and Crossville, TN. The experiment was established in summer 2014 using a randomized complete block design with three replications. Each plot within each replicate was a single row of 10 plants planted on 30-cm spacing, and rows were spaced 90 cm apart. Parental clones of 22 crosses were evaluated only in Crossville sites. Biomass yield was recorded at the end of fall 2015 and 2016. Biparental crosses were different in biomass yield (p < 0.001), and significant genotype x environment interaction for biomass yield was observed. Nineteen crosses produced 18 to 53% higher biomass compared with the average of the Alamo and Kanlow population bulks. Average yields of a matured stand ranged from 11.16 to 23.3 t ha-1. Four crosses demonstrated 25 to 41% midparent heterosis (MPH), and one cross showed 23% high-parent heterosis. Two of the crosses showed negative MPH. Heterosis in both directions suggests presence of both favorable and unfavorable complementary dominant genes in switchgrass. These findings could help improve cultivar breeding strategies in lowland switchgrass. [ABSTRACT FROM AUTHOR]

Switchgrass (Panicum virgatum L.) has been identified as a cellulosic bioenergy feedstock crop partly because of its potential to produce high biomass yields on marginal lands. Many breeding programs are focused on increasing biomass yields to improve the economic viability of the crop. However, increasing biomass yields without selecting for reduced biomass nitrogen (N) concentration will result in substantial increases in N removal at harvest. Our objectives were (i) to determine the current trajectory of biomass yield and N removal from breeding programs, (ii) to estimate the reduction in the rate of genetic gain for biomass yield when N concentration was incorporated into a breeding program, and (iii) to estimate the effects reduced N concentration might have on biofuel quality. Biomass yield and N concentration had a negative genetic correlation (-0.43), but a 50% increase in biomass yield likely will result in a 37% increase in N removal with direct selection for biomass yield. We estimated that incorporating the goal of reducing N concentration into a breeding program would result in a 225% greater reduction in N concentration while achieving 74% of the biomass yield gains achieved with direct selection for biomass yield only. Reducing N concentration in biomass was predicted to improve quality for use of biomass in a combustion system and to have minimal effects on quality in an ethanol conversion system. We conclude that simultaneous selection for increased biomass yield and reduced N concentration is both a worthy and feasible objective for switchgrass breeding programs that should improve the likelihood that improved yields from breeding are not undermined by increased N requirements. [ABSTRACT FROM AUTHOR]

Switchgrass (Panicum virgatum L.) can provide summer forage when forage production from cool-season grasses is limited. This experiment was conducted over two growing seasons (2014 and 2015) to determine nitrogen (N) fertilizer application rate and time of harvest effect on switchgrass herbage mass, nutritive value, and nutrient removal. Treatments consisted of a split-plot arrangement of five N rates (0, 45, 80, 135, and 180 kg ha-1) applied annually as main plots and harvest time (harvested in July for forage or October for biomass) as subplots in a randomized complete block design with three replications. Nitrogen rate x time of harvest interaction had no effect on herbage mass or nutritive value. Increasing N application rates increased herbage mass, crude protein, in vitro dry matter digestibility, and neutral detergent fiber concentrations, but not acid detergent fiber. A quadratic function described the relationship between herbage mass and N rate, with maximum yield occurring at 151 kg N ha-1. The economic optimum N rates ranged from 90 to 120 kg N ha-1 and depend on switchgrass hay price and N fertilizer costs. Generally, herbage mass was greater for switchgrass harvested for biomass, but nutritive value and nutrient removal were greater when switchgrass was harvested for forage. Switchgrass herbage mass and nutrient removal were greater in 2014 than in 2015. Our findings showed that N fertilizer rates for switchgrass under rain-fed conditions need to be adjusted on the basis of expected herbage mass produced, hay value, and prior year N removal rates. [ABSTRACT FROM AUTHOR]

Estimating genetic parameters is an essential step in breeding by recurrent selection to maximize genetic gains over time. This study evaluated the effects of selection on genetic variation across two successive cycles (C1 and C2) of a 'Summer'x'Kanlow' switchgrass (Panicum virgatum L.) population. Two progeny tests were planted in 2007 and 2011 near Mead, NE and respectively analyzed for 2 and 4 yr. Each test was a randomized complete block design, with four replicates of 34 halfsib families in single-row plots of 10 seedlings in C1 and with three replicates of 111 halfsib families in single-row plots of fve seedlings in C2. The C2 test included C0, C1, and parental populations for comparison. Multivariate mixed linear models revealed ample additive genetic variation for dry matter yield (DMY), Klason lignin (KL), and predicted ethanol yield (ETOH) in both cycles, with heritability ranging from 0.40±0.18 to 0.5±0.14 at the family level, from 0.22±0.17 to 0.36±0.22 at the individual level, and from 0.25 to 0.31 within family in C1. Matching values in C2 were: from 0.42±0.09 to 0.63±0.07, f rom 0.10±0.07 to 0.34±0.13, and from 0.12 to 0.48. More opportunity exists to improve DMY, with a coefficient of additive genetic variation of 11 to 32%, than KL (3-5%) or ETOH (3-6%). The traits were properly aligned for joint improvement for high DMY and reduced KL in C1, owing to favorable genetic correlations (rA=-0.33±0.11) and each having respective rA of 0.60±0.05 and -0.62±0.07 with ETOH. In C2, the rA between DMY and KL (-0.19±0.10) or ETOH (0.04±0.04) decreased towards zero, and that between KL and ETOH was moderately less negative (-0.35±0.15) . These results suggest a strong genetic basis for improvement of the traits and monitoring of their patterns every cycle to fnd the proper weights that maximize the breeding goal of designing the ideal bioenergy switchgrass. [ABSTRACT FROM AUTHOR]

Switchgrass (Panicum virgatum L.) is undergoing development as a biomass crop to support conversion of cellulosic biomass to energy. To avoid the competition of biomass with food or feed crops, most commercialization proposals suggest that switchgrass should be grown exclusively on marginal lands that are not fit for food or feed production. The objective of this study was to investigate the potential for cultivar × environment interactions that would affect the methods and approaches for breeding and evaluating switchgrass cultivars, including both upland and lowland types, for high-input versus low-input types of environments. Biomass yield was measured on 14 cultivars that were present in 28 replicated field experiments representing seven regions, ranging from 75 to 100° W and spanning USDA Hardiness Zones 4 through 7. Region was the most important environmental factor interacting with cultivars, supporting the idea that the north-central and northeastern United States should have independent switchgrass breeding programs. Cultivars interacted with soil phosphorus concentration in New Jersey and with depth of the A and B horizons in New York and showed mild interactions with rate of nitrogen fertilizer at several locations. Cultivar rank correlation coefficients between the two rates of nitrogen fertilization (100 vs. 0 kg N ha-1) ranged from 0.23 to 0.88, suggesting a possible benefit to breeding and selection without applied nitrogen fertilizer. [ABSTRACT FROM AUTHOR]

Six generations of divergent breeding in switchgrass (Panicum virgatum L.) for forage in vitro digestibility (IVDMD) resulted in significant changes in 20 biomass composition traits. Stepwise multiregression was used to determine which of the 20 composition traits had the largest significant effects on forage IVDMD and potential ethanol yield (ETOH) in a biorefinery. Switchgrass biomass samples from a field nursery containing the divergent switchgrass populations and families were harvested after flowering, dried, ground, and analyzed for composition traits by near-infrared reflectance analyses using previously developed near-infrared reflectance calibrations. After nonsignificant variables were eliminated, the resulting multiple regression models were highly significant (P < 0.001) and accounted for 95 and 96%, respectively, of the total variation for both IVDMD and ETOH. Standardized partial regression coefficients were used to estimate the relative importance of each significant variable. The biomass composition factors that had the largest impact on both IVDMD and ETOH were esterified ferulates, p-coumarate esters, specific cell wall sugars that are involved in the linkage of cell wall lignin to hemicellulose, N, and extracted fats. Klason lignin was not a significant variable in either regression analysis, even though it was strongly negatively correlated with both IVDMD and ETOH. The IVDMD test, which acted as a biological selection index in a long-term population breeding program, impacted an array of switchgrass biomass composition traits whose relative effects on both IVDMD and ETOH had not been previously quantified. [ABSTRACT FROM AUTHOR]

Switchgrass (Panicum virgatum L.) is an important emerging biofuel crop. In breeding nurseries, plants are typically widely spaced; however, production is in densely planted swards. This disconnect may hinder cultivar improvement. This study measured the efficiency of low-density, spaced-plant selection on improving biomass and ethanol yield in a high-density, simulated sward. Fifty-six full-sib families were clonally replicated in two adjacent nurseries in Knoxville, TN. The spaced-plant nursery consisted of single plants on 1-m centers. The simulated-sward nursery was created by planting four by seven plants on 0.33-m centers with 1-m alleys. In 2013 and 2014, biomass yield, ethanol yield, and morphological traits were evaluated. Trait means, correlations, and efficiency of indirect selection (E) were calculated. Significant interaction (p < 0.05) between year and nursery was observed for all traits except ethanol yield. The identified high-yielding ideotype differed between biomass and ethanol yield and between spaced-plant and simulated-sward nurseries. Selection under spaced-plant conditions for simulated-sward performance was efficient for ethanol yield (E = 0.96) but highly inefficient for biomass yield (E = −0.31). Several morphological traits evaluated under spaced-plant conditions were identified as efficient indirect selectors for simulated-sward biomass or ethanol yield. Results suggest selections for sward biomass yield may be more appropriate under sward-like conditions, but that spaced-plant nurseries are efficient for selection of ethanol yield performance under sward-like conditions and for indirect selection of sward yield traits using morphological traits. [ABSTRACT FROM AUTHOR]

Switchgrass (Panicum virgatum L.) takes 3 yr to reach maximum biomass yields, delaying selection and cultivar improvement. This study evaluated the efficiency of early selection in improving third-year biomass and ethanol yields in lowland switchgrass. Fifty-six full-sib families were planted in Knoxville and Crossville, TN, with 1-m spacing in a randomized complete block design. In 2012 to 2014, plants were evaluated for biomass yield, ethanol yield, and morphological traits at 8 wk after emergence and in years one through three. Trait means, efficiency of indirect selection, and genetic gain were calculated. Biomass yield differed significantly by year (92 g in yr 1, 1069 g in yr 2, and 1425 g in yr 3) while ethanol yield did not (... = 63 mg g-1). Juvenile selection was ineffective. Biomass selection was most efficient using first-year fall height with genetic gains per year 2.4 times those of direct selection on third-year biomass. First-year biomass and second-year biomass, fall height, spring height, and tiller diameter also exhibited high efficiency (1.3 to 1.9). For ethanol yield, negative efficiency indicated selection for low first-year height and low second-year spring height, and tiller diameter would result in 1 to 1.3 times the genetic gain expected from direct selection on third-year ethanol yield. Results indicate that early selection and indirect selection using morphological traits may speed yield improvement due to greater selection efficiency and higher genetic gains. [ABSTRACT FROM AUTHOR]

Establishment failures are a challenge to widescale use of switchgrass (Panicum virgatum L.) for biomass feedstock and/or forage production. Small grain cover crops, because of their allelopathic properties, may inhibit (direct allelopathy) or enhance (competition reduction) switchgrass establishment, and provide indirect benefits such as soil conservation and forage/ grain production during the establishment year. Objectives of this study were to evaluate stand density and yield based on seeding switchgrass into (i) four small grain cover crops: wheat (Triticum aestivum L.), cereal rye (Secale cereale L.), barley (Hordeum vulgare L.), oat (Avena sativa L.), and fallow control at (ii) three dates (15 March, 1 May, and 10 June) that approximated typical timing for removal of small grain cover, haylage, or grain crops in Tennessee, respectively. Treatments were assigned in a split-plot design with three replications at three locations in Tennessee in 2008 and repeated in 2009. Small grain cover crops influenced (P = 0.002) switchgrass seedling density at only one location (wheat > other small grains > control) and interacted with year at another, but was never related (P < 0.05) to yield. Planting date affected switchgrass density and yield, but always in the context of an interaction with year; yield varied by location and year with no clear pattern. Density also varied by year and location, with fewer plants occurring during May seeding dates. Therefore, switchgrass can be planted following small grains without an apparent penalty or advantage to switchgrass stand density or yield, while offsetting lost production during establishment. [ABSTRACT FROM AUTHOR]

Switchgrass (Panicum virgatum L.) is a dedicated energy crop native to tallgrass prairie and savanna ecosystems of North America. Although high biomass yield is of significant importance for the development of switchgrass as a bioenergy crop, mineral nutrients in biomass are critically important for sustainable bioenergy crop production but are detrimental for thermochemical conversion of biomass to energy. To evaluate biomass yield and nutrient uptake or nutrient cycling in switchgrass cultivars, replicated trials across three sites (Arlington, WI; Marshfield, WI; and Urbana, IL) were established in 2009. The switchgrass cultivars were harvested once annually at upland peak, after killing frost, or post-winter in the spring from 2010 to 2014. Switchgrass biomass yield was greatest at the upland peak harvest, averaging 9.9 Mg ha-1 with biomass decreasing as harvest was delayed. Similarly, nutrient content in the biomass was greatest at the upland peak harvest with N, P, and K at 69, 77, and 23 kg ha-1, respectively. The majority of the N, P, and K in the biomass at the upland peak harvest was absent from the biomass at the post-frost harvest. The lower levels of nutrients and total ash in the biomass at the post-frost harvests will be beneficial for downstream conversion to bioenergy and may also reduce the future fertilizer requirements of the biomass crop. [ABSTRACT FROM AUTHOR]

It is hypothesized that switchgrass (Panicum virgatum L.) remobilizes phosphorus (P) and potassium (K) to belowground plant organs during maturation and senescence. Consequently, recommended biomass harvests occur after the first killing frost or early November, although field curing conditions at that time may be undesirable. Therefore, the objectives of this study were to determine i) if harvests can occur earlier based on removal of P and K (in leaves and stems) for two standard ('Alamo' and 'Kanlow') and eight new upland and lowland cultivars during the fall (i.e., mid-September, mid-October, late October, and early November) in Exp. 1, and ii) changes in P and K concentration in aboveground versus belowground biomass (roots, crowns, and shoots) in standard cultivars during mid- September, late October, and mid-November in Exp. 2. Both experiments were performed in a randomized complete design with three blocks at Knoxville and Springfield, TN, USA, in 2009 and 2010. Shoot P and K concentrations in cultivars did not decline from mid-September to late October, nor did P and K in crowns and roots increase from mid-September to mid-November (P > 0.05). However, leaf concentrations of P (across locations and years) were greatest for OK NSL-2001-1 (lowland cultivar), which did not differ from Blackwell (upland cultivar). Cultivar Kanlow had the lowest P concentrations across all plant parts and cultivars. Similarly, stem P was greatest for the cultivar Blackwell. Harvest timing of upland and lowland switchgrass cultivars may therefore be extended to earlier in the fall (mid-September) based on lack of attenuating declining trends of P and K in shoots of switchgrass cultivars in the Southeast. [ABSTRACT FROM AUTHOR]

Efficient conversion of biomass crops to energy requires an understanding of plant quality, including cell wall and mineral composition. We compared key quality parameters of two leading switchgrass (Panicum virgatum L.) varieties, lowland 'Kanlow' and upland 'Cave-in-Rock', over two growing seasons and across five landscape positions. Through a nonmetric multidimensional scaling (NMS) analysis, wherein two ordination axes together explained most of the variation in the data (r2 = 0.89), we found plant mineral composition (N and ash concentrations ) was influenced more by landscape position, while plant cell wall components were affected more by year of growth. Switchgrass at the floodplain position was "dirtier," containing greater ash concentration (110 g kg-1) and N concentration (6.2 g kg-1) known to contaminate biochemical and thermochemical pathways. Furthermore, variety influenced quality; for example, Kanlow had less lignin than Cavein-Rock, but all biomass had greater lignin in 2011 than in 2010. Kanlow and Cave-in-Rock contained greater concentrations of total nonstructural carbohydrates (TNC) in 2010 than in 2011 by as much as 8 and 20%. While considerable work has focused on breeding for improved quality and regional-scale environmental effects, our results indicate that variety also significantly interacts with subfield-scale environmental and interseasonal effects. [ABSTRACT FROM AUTHOR]

Establishment failures linked to seed dormancy are a challenge to wide-scale use of switchgrass (Panicum virgatum L.) for biomass feedstock and forage production. One prospective strategy for breaking dormancy is dormantseason planting. The objectives of this study were to evaluate (i) three switchgrass dormantseason planting dates (1 December, 1 February, and 15 March) vs. a growing-season (1 May) control; (ii) two seeding rates (6.7 and 10.1 kg pure live seed [PLS] ha-1); and (iii) highand lowdormancy seed lots. Treatments were assigned in a split-plot design with three replications at two locations in Tennessee in 2008 and 2009. Neither seeding rate nor seed-dormancy level affected plant density or yield (P > 0.05). However, a seeding date × year interaction impacted first-year density at both locations. Although patterns differed by year for the two locations, density of March plantings equaled or exceeded (P < 0.05) those at other dates for both locations and years. These variations in density did not carry over to impact yield in year two. A sigmoidal regression of seedling density vs. yield was significant (P < 0.001) albeit not strong (R2 = 0.13); yield response approached an asymptote above ~8 plants m2. Results suggest March planting dates, using standard seeding rate recommendations (6.7 kg PLS ha-1) irrespective of seed-dormancy rates, may be more reliable than planting in May. Thus, a broader establishment window than traditionally used may be practical. However, results should be validated over a broader range of soils and climatic conditions, especially over a winter severity gradient. [ABSTRACT FROM AUTHOR]

Switchgrass (Panicum virgatum L.) breeding and selection have enhanced the agronomic qualities of this species as a crop for forage and bioenergy applications. previous work has characterized variation in phenotypic traits (e.g., survival, biomass yield, and cell wall carbohydrates) among wild and cultivated populations. Despite the importance of low dormancy to the establishment of a productive switchgrass stand, there is little information characterizing the dormancy of selectively bred cultivars vs. wild populations of switchgrass. The objectives of this study were to use growth chamber experiments to quantify germination vs. dormancy (confirmed by tetrazolium tests) of eight wild and four cultivar populations and evaluate the relationship between seed size and germination. While cultivars generally showed higher germination than wild populations, there was marked variation in germination among wild populations; for those with lower germination, the ungerminated fraction comprised mostly live (i.e., dormant) seeds. These data led us to perform a subsequent experiment testing the application of a seed treatment, cold-moist stratification, on a subset of eight populations representing the wide variation in germination observed in the first experiment. Cold-moist stratification substantially increased germination, but the magnitude of the effect varied among populations. populations with higher dormancy showed a much larger increase in germination after cold-moist stratification. These data clearly show that seed dormancy in wild populations can be easily overcome by cold-moist stratification in the short term and breeding and selection in the long term. [ABSTRACT FROM AUTHOR]

Switchgrass (Panicum virgatum L.) is an important native grass and dominant member of the tallgrass prairie ecosystem. It is used for conservation, restoration, livestock feed production, and bioenergy feedstock production. The purpose of this review is to describe the biological and geographical basis for switchgrass germplasm diversity and to provide a resource for scientists and outreach personnel to find switchgrass germplasm to meet their needs. Upland and lowland ecotypes represent the most important polymorphism in switchgrass, with distinct but overlapping geographic distributions. Variation in ploidy exists within both ecotypes, with 2n = 4x = 36 the dominant ploidy in the lowland ecotype and 2n = 8x = 72 the dominant ploidy in the upland ecotype. Ploidy is a strong barrier to gene flow, but ecotype is a weak barrier, with up to 10% of random individuals demonstrating some evidence for upland-lowland hybridization in their ancestry. Latitudinal and, to a lesser extent, longitudinal differentiation exists within each ecotype, such that most wild populations and cultivars are not well adapted more than one hardiness zone from their place of origin. Plant breeding can alter this relationship by creating populations with improved cold tolerance, for example, increasing the adaptation range of an individual cultivar. The USDA National Plant Germplasm System maintains the national switchgrass collection, which is available for research and breeding purposes. [ABSTRACT FROM AUTHOR]

Switchgrass (Panicum virgatum L.) has been identified as a model perennial grass species to compete with alternative sources for providing biomass to fulfill cellulosic biofuels provisions of the US Energy Independence and Security Act of 2007. The objective of this study is to determine the value of a more productive switchgrass variety relative to that of the best available alternative. Biomass data were produced in an experiment with four commercial switchgrass cultivars (Alamo, Blackwell, Kanlow, and Cave-in-Rock) and five experimental lines over 4 yr at Stillwater, OK. One of the experimental lines, Cimarron, was released as a cultivar in 2008 during the experiment. The remaining four experimental lines were NL93-2, NSL 2001-1, NL 94-2001-1, and NSU 95-2001. An ANOVA model is used to test for differences in switchgrass yield. Enterprise budgets are used to calculate net returns and stochastic efficiency analysis is used to investigate yield risk. For a farm-gate biomass price of $50 Mg-1, expected net returns were estimated to be $80 ha-1 yr-1 greater in postestablishment years for Cimarron than for Alamo. Assuming a year for establishment, nine postestablishment production years, a farm-gate biomass price of $50 Mg-1, a discount rate of 6.5%, and environmental conditions similar to those that prevailed during the field experiment, the net present value of seeding a field in the region to Cimarron rather than Alamo would be $501 ha-1. [ABSTRACT FROM AUTHOR]

Apart from the importance of switchgrass (Panicum virgatum L.) as forage for livestock, it is useful as a high-value cellulosic biofuel feedstock. Breeding for a biofuel crop is complicated by the existence of multiple platforms for conversion of biomass to energy. Our main objective was to investigate the relative merits of single-trait selection, correlated response to selection, and Smith-Hazel-index-based selection for the following traits: biomass dry matter yield (YLD), ethanol (ETOH), Klason lignin (KL), and high heating value (HHV). The genetic analysis was based on a 2-yr data set generated from evaluation of 144 half-sib (HS) families in sward-plot trials at Arlington and Marshfield, WI. There was significant (P < 0.05) additive genetic variation among the families for all traits and for family × site interaction for the traits HHV and YLD. The estimates of narrow sense heritability on a HS family mean basis ranged from 0.37 for YLD to 0.51 for KL. Genetic correlation of YLD with ETOH, HHV, and KL were 0.38, 0.27, and 0.01, respectively. The index constructed to increase YLD and ETOH and reduce KL was most successful for a fermentation platform. This index enabled identification of families for enhancing ethanol production that would have been missed if selection was based solely on YLD. The index weighted to increase YLD and KL best suited a combustion platform. Both of these two indices had economic impacts superior to any other selection index evaluated. [ABSTRACT FROM AUTHOR]

Switchgrass (Panicum virgatum L.) is a candidate for cellulosic bioenergy feedstock development in many parts of North America. Because production costs are generally considered too high for economic and sustainable production of switchgrass biomass, breeding for increased biomass yield is a viable and desirable research objective. The objective of this study was to estimate heterosis and reciprocal-cross effects in three types of switchgrass crosses: upland × upland (U×U), lowland × lowland (L×L), and upland × lowland (L×U) hybrids. A total of 62 hybrids and two parental populations were evaluated for 2 yr at two Wisconsin locations. Mid-parent heterosis for biomass yield was observed in only four L×L hybrids and no L×U hybrids, suggesting that it is not a universal phenomenon between upland and lowland ecotypes. Reciprocal effects were more important than heterosis effects, as most hybrids were similar in performance to their maternal parent population. Flowering time was a strong driver of biomass yield, accounting for 67% of the variation among hybrids in biomass yield and increasing biomass yield by 0.47 Mg ha-1 for each day delay in flowering time. [ABSTRACT FROM AUTHOR]

A modified form of restricted, recurrent phenotypic selection was used to select for seedling shoot weight in switchgrass (Panicum virgatum L.), big bluestem (Andropogon gerardii Vitman), and indiangrass [Sorghastrum nutans (L.) Nash] populations for three generations. Seedlings were grown in micropots in trays in a greenhouse and were individually clipped and weighed 4 wk after emergence. The seedlings were allowed to regrow, and the heaviest seedlings were transplanted to field nurseries for polycrossing to produce Syn 1 seed. Three breeding cycles were conducted for each grass. After the third breeding cycle, Syn 2 generation seed was produced for each cycle, including cycle 0 for 2 yr, and was used in subsequent greenhouse and field evaluations to determine if the breeding procedure improved seedling vigor as measured by seedling shoot weight. In two greenhouse evaluation trials, the increase in seedling weight per cycle was 7.8, 5.6, and 10.2% for big bluestem, switchgrass, and indiangrass, respectively. In two field trials, seedling weight also increased with successive cycles of selection except for indiangrass in one trial. Establishment success as measured by stand counts did not differ among the cycles of selection for the three grasses in the field trials. Based on these results and the results of subsequent breeding and field evaluation work on seedling tiller number, it is apparent that seedling traits of these grasses can be modified by breeding. To improve establishment of these grasses, research on developing agronomic seed production practices that result in improved seed quality would also be beneficial. [ABSTRACT FROM AUTHOR]

Switchgrass (Panicum virgatum L.) cultivar research is focused on improvement in biomass yield and feedstock composition for bioenergy use. These improvements could be achieved by exploiting additive and non-additive effects of nuclear genes, as well as reciprocal differences. The objective of this study was to evaluate the influence of reciprocal effects on biomass yield in lowland switchgrass. Forty-six biparental crosses and their reciprocals were evaluated at two locations in south-central Oklahoma using a honeycomb design. The trial was established in the summer of 2007, and year-end biomass yields were recorded during 2008 and 2009. The mean DNA content of the parents ranged from 1.96 to 3.70 pg, confirming that the parental genotypes were tetraploid. Ten of the 46 crosses demonstrating favorable reciprocal effects (P ≤ 0.10) had >12% biomass yield advantage. The direction of reciprocal difference was fairly consistent across locations by years. The relative advantage of using a certain genotype as the female parent depended on the genetic background of the other genotype used in crossing, indicating the complex genetics of reciprocal effects. The hybrids from parent 'LL43' in crosses with 'LL126' and 'LL22' produced an average of >40% biomass when used as the pollen parent rather than using it as the female. Evaluation of genotypes of interest for reciprocal effects by crossing with several other genotypes would help identify parents with favorable maternal effects for use in development of superior synthetic or hybrid varieties. [ABSTRACT FROM AUTHOR]

Commercial viability of switchgrass (Panicum virgatum) as a biofuel will require further improvements of biomass yield to improve sustainability. Direct selection for biomass yield in switchgrass has proven difficult due to the many factors influencing biomass yield. The identification of morphological traits associated with biomass yield could increase the efficiency of breeding efforts if these traits can be used as indirect selection criteria. By allowing increased screening and greater intensity of selection for biomass yield within spaced-plant nurseries, these results may impact how phenotypic selection is used for switchgrass cultivar development. The objective of this research was to identify morphological traits in parental plants that are predictive of biomass yield in progeny swards. Results of this research demonstrate the challenges of selecting for increased biomass yield in switchgrass within spacedplant nurseries. Limited predictive ability was observed using individual and combinations of plant morphological traits. Comparisons of models with varying subsets of traits revealed common traits among the best predictive models including plant height, single-plant dry biomass, and second leaf width. Predictions of single- plant biomass, using the same set of morphological traits, revealed a large effect for tillering related traits. The observation that different traits affect biomass yield differently in the two planting types may indicate an effect of plant competition on the relationship of these traits with biomass yield. While these traits can help guide selections for a preferred plant ideotype, additional efforts to improve selection schemes for increasing biomass yield will be necessary for sustained genetic gain in switchgrass. [ABSTRACT FROM AUTHOR]

Major efforts are currently being undertaken to improve biomass yield in switchgrass. Amongand- within-family selection has been proposed as an efficient selection scheme to increase rates of genetic gain. The objectives of this study were to estimate the heritability of three yield-related traits (plant height, tiller count, and flowering date) and evaluate the suitability of those traits as within-family-selection criteria. Divergent selections of parents were made for each trait from an upland-tetraploid population developed for use in temperate North America. Progeny from these selections were used to estimate narrow-sense heritability by both parent- progeny regression and response to selection. Moderate heritability (0.41) was estimated for plant height but was greater for selection of increased height. Heritability for tiller count was low overall (0.06), with greater values observed for reduced tillering selections. Flowering date was estimated to have high heritability (0.75) overall in both selection directions. Plant height and flowering date both appear heritable on a spaced-plant basis and may be effective selection criteria for within-family selection. The relative value of among-and-within-family selection within a practical breeding program will vary depending on what selection criteria are used and the timing of selections. [ABSTRACT FROM AUTHOR]

Switchgrass (Panicum virgatum L.) is a candidate for cellulosic bioenergy feedstock development in many parts of North America, Europe, and Asia. Breeding for increased biomass yield is a viable and desirable research objective to improve both economic and energy yields per hectare. The objectives of this study were to estimate progress from (i) selection for biomass yield in upland switchgrass, (ii) selection for winter survival, biomass yield, and biomass quality in lowland switchgrass, and (iii) advanced-generation heterosis effects in four upland × lowland hybrid switchgrass populations. Selection for increased biomass yield in upland switchgrass resulted in mean genetic gains for of 0.71 Mg ha-1 per cycle (8% per cycle = 4% yr-1) for biomass yield. Selection for increased biomass yield in lowland switchgrass resulted in mean genetic gains of 0.89 Mg ha-1 (18% = 1% yr-1) for biomass yield. Mean high-parent heterosis between upland and lowland ecotypes was 3.57 Mg ha-1 (43%). These gains in biomass yield resulted in significant increases in ethanol production for a fermentation platform or high heating value for a combustion platform. Biomass yield is a moderately heritable trait in switchgrass and it can be readily improved in both upland and lowland populations using conventional breeding methods. [ABSTRACT FROM AUTHOR]

Switchgrass (Panicum virgatum L.) has potential for both bioenergy and forage. The objectives of this experiment were to (i) determine whether switchgrass could be harvested for greater nutritive value during the vegetative stage relative to early reproductive growth (boot stage); (ii) compare biomass yields of switchgrass harvested once vs. twice per year for bioenergy; and (iii) examine effects of N fertilizer rates on harvest systems. The experiment was a randomized complete block design with a splitplot arrangement of harvest system treatments as main plot (harvest once per year after frost, harvest twice per year first at vegetative or boot stage, and regrowth after frost) and N fertilizer rate as subplots (0, 90, 180, and 270 kg N ha-1). Biomass yield was greatest and nutrient concentrations were least in the one-cut system. For the two-cut system, nutritive values and yields were similar. Total annual biomass increased linearly with N fertilization. Across N rates, crude protein (CP) concentration for the two-cut systems was 50% greater (71 g kg-1) and acid detergent fiber (ADF) and neutral detergent fiber (NDF) concentrations were 20% lesser (465 and 856 g kg-1, respectively) than switchgrass in the one-cut system. -Switchgrass harvested at vegetative through boot stage and its regrowth could provide forage of acceptable nutritive value to beef cows. However, greater nutrient removal requires appropriate soil fertility evaluation and fertilizer management for sustainable yields. [ABSTRACT FROM AUTHOR]

Weed control during the establishment year of switchgrass (Panicum virgatum L.) is critical for a successful stand. Laboratory and field studies were conducted for 2 yr to evaluate the effectiveness of seed safeners for protecting switchgrass seed from the preemergent herbicide metolachlor. Initial evaluations of six seed safeners determined that fluxofenim was the only successful protectant tested for switchgrass seedling germination. Safener rates 0, 25, 50, and 100% of the recommended rate (40 mg a.i. 100 g per seed), method of application (coating vs. controlled hydration), ecotype (lowland vs. upland), dry matter yield, and number of crowns per row were analyzed in replicated field trials conducted in Starkville, MS, Ames, IA, Blacksburg, VA, and Brookings, SD, in a randomized complete block design. Two establishment years were planted in single-row (6.1 m) plots spaced 50.8 cm apart. Subsequent biomass yield was harvested at the end of each growing season. Exceptional stands were achieved with all rates of safener in both years due to the reduction or elimination of annual grassy weeds and no crop injury was experienced at any test location. The controlled hydration (combination of 25, 50, or 100% fluxofenim) method resulted in significantly greater yields and crown counts than the coating technique at most locations for both years. [ABSTRACT FROM AUTHOR]

Switchgrass (Panicum virgatum L.) is a North American grass that is being improved through conventional breeding and genetic engineering to create a biofuel feedstock. However, the introduction of novel traits has created concerns about pollen-mediated gene flow and negative environmental impacts. The objective of this study was to model switchgrass pollen dispersal using a Lagrangian approach informed by data on pollen longevity and size. With outdoor exposure, the viability of pollen from three cultivars declined over 60 min, but rare events showed pollen longevity of up to 100 min. To model pollen dispersal, wind fields were measured in two locations and on two dates to create case studies representing light wind conditions with buoyant turbulence or stronger winds with pressure-driven, nonturbulent conditions. In the first case study, switchgrass pollen entrained in light wind conditions with buoyancy-driven turbulence moved up to approximately 3.5 km from the source with a maximum flight time of 6000 s. In the second case study, pollen released in stronger winds with pressure-driven conditions moved up to approximately 6.5 km with a maximum flight time of approximately 1300 s. In both cases, the majority of pollen grains were deposited closer to the source. These case studies provide information helpful for predicting pollen-mediated transgene flow, isolating field trials, creating containment and coexistence strategies, and conserving valued switchgrass populations in coastal areas and prairies. [ABSTRACT FROM AUTHOR]

Two breeding systems, between- and withinfamily selection (BWFS) and multistep family selection (MFS), were compared using three switchgrass (Panicum virgatum L.) populations to determine which system was the most effective in improving biomass yield and in vitro dry matter digestibility (IVDMD). With BWFS, half-sib families are produced and evaluated on a family basis and then the best plants within the best families are selected for crossing to produce a new strain. With MFS, parent genotypes of the half-sib families being evaluated in the BWFS selection nursery are maintained and the genotypes whose progeny were the best in the BWFS evaluation trial are selected and polycrossed to produce a new strain. Methods were compared using two populations in which improved biomass yield and IVDMD were the selected traits and with a population for which improved IVDMD and winter survival were the selected traits. For the populations for which yield was a selection criteria, the BWFS breeding system produced strains with significantly greater biomass yields than the MFS system. For one of these populations, the BWFS and MFS systems did not differ for IVDMD but the MFS system produced a strain with higher IVDMD for the other population. For the population in which IVDMD and winter survival were the selection criteria, the BWFS strain had greater IVDMD than the MFS strain. Overall, the BWFS system was superior and required less work. [ABSTRACT FROM AUTHOR]

Biomass composition of switchgrass (Panicum virgatum L.) can affect its utilization by ruminants and its conversion to liquid fuels in a biorefinery. The objective of this study was to evaluate the effects of six generations of divergent breeding for forage in vitro dry matter digestibility (IVDMD) on switchgrass biomass composition, forage quality traits, and ethanol yield. Initially there was one cycle of selection for both low (C-1) and high IVDMD (C1 = cv. Trailblazer), followed by four additional breeding cycles for high IVDMD. In cycles 4 and 5, winter survival was included as a selection criterion because of decreased winter survival of the C3 population. The experimental populations that were produced by these breeding generations and nine half-sib families from cycle 5 were evaluated for two post-establishment years at the research station in eastern Nebraska, where all the breeding work was conducted. The six breeding generations resulted in significant differences among the populations for all the 28 cell wall and non-cell-wall composition variables measured, forage quality, and ethanol yield traits measured except for total biomass C, cell wall concentration, soluble glucose, and etherified ferulates. These traits included all cell wall and nonstructural carbohydrates. Breeding for the heritable complex trait IVDMD affected a large number of plant biomass characteristics and also adversely affected plant biomass yield and winter survival. [ABSTRACT FROM AUTHOR]

Switchgrass (Panicum virgatum L.) is typically slow and difficult to establish. Field experiments evaluated switchgrass establishment and the response of warm-season grass weeds (large crabgrass [Digitaria sanguinalis (L.) Scop.], broadleaf signalgrass [Urochloa platyphylla (Munro ex C. Wright) R.D. Webster], Johnsongrass [Sorghum halepense (L.) Pers.], and Texas panicum [Urochloa texana (Buckley) R.D. Webster]) to a preemergence (cloransulam) or postemergence (foramsulfuron, pendimethalin, quinclorac, foramsulfuron + pendimethalin + quinclorac, nicosulfuron, nicosulfuron + pendimethalin + quinclorac, nicosulfuron + quinclorac + atrazine, and monosodium methanearsonate [MSMA]) herbicides. Experimental design was a split-split-plot design with presence/absence of preemergence herbicide cloransulam as main plot, weed species as subplot treatment, and postemergence herbicides as sub-subplot treatments. Herbicides foramsulfuron + pendimethalin + quinclorac was applied at the 1- to 2- and 2- to 3-leaf stage, whereas nicosulfuron was applied at 2- to 3-leaf stage and nicosulfuron combinations and MSMA were applied at 3- to 4-leaf stage. Using cloransulam as a preemergence herbicide resulted in lower switchgrass seedling numbers and generally did not improve establishment. Interseeding Johnsongrass allowed for the greatest number of switchgrass seedlings and was the least competitive weed, whereas interseeding large crabgrass resulted in the least amount of switchgrass and proved to be the most competitive weed. Foramsulfuron + pendimethalin + quinclorac resulted in effective weed control (>70%) for all four species evaluated and improved switchgrass establishment (13-26%) compared to the untreated control (0-3%); however, greater improvement in stand establishment is needed. [ABSTRACT FROM AUTHOR]

Perennial, warm-season grasses cut for hay frequently have inadequate crude protein (CP) concentrations for acceptable ruminant performance. This study determined the influence of alfalfa (Medicago sativa L.) as a CP supplement to steers (Bos taurus) fed switchgrass (Panicum virgatum L.) hay harvested at the early-heading stage. Diets of 100% switchgrass (SG) and 100% alfalfa (AL) were included along with 25, 50, and 75% mixtures of the hays making five treatments. Steer dry matter intake (DMI), whole tract dry matter digestibility (DMD), eating behavior, and masticate characteristics were estimated. Steer DMI averaged 1.35 kg 100 kg-1 body weight (BW) for 100% SG and increased linearly (P < 0.01) to 2.93 kg 100 kg-1 BW for 100% AL. Also, DMD increased linearly (P < 0.01) from 484 g kg-1 for 100% SG to 653 g kg-1 for 100% AL. Concentration of CP was 51 g kg-1 for SG and increased quadratically (P < 0.01) to 241 g kg-1 with increasing AL while neutral detergent fiber (NDF) decreased quadratically (P < 0.01) from 792 g kg-1 for SG to 407 g kg-1 for AL. Masticate in vitro dry matter disappearance (IVDMD) increased quadratically (P < 0.01) from 509 g kg-1 for SG to 660 g kg-1 in AL whereas CP increased linearly (P < 0.01) from 60 g kg-1 for SG to 230 g kg-1 in AL. Increasing AL of the as-fed hay linearly decreased (P < 0.01) chews per gram of dry matter, IVDMD, and CP but increased quadratically (P < 0.01) chews per gram of NDF. Steers readily ate the SG:AL combinations; AL could thus provide a source of CP for SG based diets. [ABSTRACT FROM AUTHOR]

Switchgrass (Panicum virgatum L.) is an important candidate for bioenergy feedstock production, prompting significant efforts to increase the number of breeding programs and the output of those programs. The objective of this experiment was to determine the potential utility of natural selection for survivorship in switchgrass swards as a tool for improving efficiency of progeny-test-based recurrent selection programs in switchgrass. One hundred random surviving plants were selected from 5-yr-old plots of six cultivars grown at five locations. Progeny of each population were grown in a four-location field experiment in Illinois and Wisconsin in direct comparison to their parent populations. On average, natural selection for survivorship increased biomass yield by 6.7%. The northernmost (i.e., coldest) selection location had the greatest response among the five locations (13.2%) while the most genetically diverse cultivar had the greatest response among the cultivars (23.5%). Results were highly variable among cultivars and selection locations, but there were no significant negative responses, suggesting that the genetic correlation between survivorship and biomass yield in switchgrass ranges from zero to some positive value. Selection for survivorship within switchgrass sward plots has the potential to improve efficiency of family-based selection methods designed to improve biomass yieldpotential. [ABSTRACT FROM AUTHOR]

Prairie cordgrass (Spartina pectinata Link) has potential for biofuel production in soils too wet for switchgrass (Panicum virgatum L.). However, poor seed set is a major impediment to seed production in this species. Our objectives were to (i) estimate frequency of seed set (i.e., normal caryopsis in spikelet) and seed predation by insects and (ii) partition variance for seed set into environmental and morphological sources for a population of prairie cordgrass selected for biofuel production. During 2005 through 2011, panicles were collected from nurseries of the selected population in South Dakota and Illinois. Seed set was 79% for 1- and 2-yr-old stands indicating neither poor seed set or seed predation, which ranged from 0 to 15%, by Aethes spartinana (Barnes & McDunnough) (Lepidoptera: Tortricidae) seriously limited seed production. Most of the variation in seed set could be accounted for by variation among and within panicles within nurseries. Spikes in the distal two-thirds of the panicle had higher seed set and lower seed predation than those in the proximal one-third. However, variance between spikes from similar panicle positions accounted for more of the variation in seed set than any other spatial or morphological source. Therefore, increased understanding of seed set, which is subject to environmental vagaries from heading through seed development, will require sampling emphasis at the spikes within panicles and spikelets within spikes levels. [ABSTRACT FROM AUTHOR]

Switchgrass (Panicum virgatum L.) needs significant biomass yield improvement for its viable use as bioenergy feedstock. Conventional family evaluation under sward plot is very effective in cultivar improvement, but it is time and resource consuming. Family evaluation under space planting using honeycomb design can reduce time and inputs. The objective of this study was to compare conventional sward-plot and modified space-plant evaluation of half-sib families in their biomass yield gain and resource use. Using same initial set of genotypes selected from 'Alamo', two experimental synthetics were developed by the following methods: (i) summer field polycrossing of selected genotypes to produce half-sibs, half-sib family evaluation under sward plot conditions (HSSward) at two locations for 2 yr, and polycrossing the five genotypes showing superior half-sibs to produce the experimental and (ii) greenhouse polycrossing genotypes during the winter to produce half-sibs, half-sib family evaluation under space-plant conditions using honeycomb design (HSSpace) for 2 yr at one location, and polycrossing the five best progeny within the five superior half-sibs to produce the experimental. The 2 to 3 yr biomass yield performance of two experimentals across five locations demonstrated that both HSSward and HSSpace led to a significant biomass yield gain over Alamo in three and two of the five locations, respectively. The HSSward produced a superior and more stable synthetic across a wide region than HSSpace. However, the HSSpace produced its synthetic a year sooner and was more resource efficient and, under finite resources, it could be a method of choice for cultivar development especially for a narrow geographic region. [ABSTRACT FROM AUTHOR]

Switchgrass (Panicum virgatum L.) grown in marginal soils may frequently be subjected to water deficit conditions. The study was designed to determine physiological response, cell wall components, and expression of genes involved in cell wall biosynthesis of switchgrass under short-term drought stress and recovery. Grasses were exposed to drought for 4 d in 2007 (Exp. 1) and 7 d in 2008 (Exp. 2) in a greenhouse and then rewatered for 1 d in both experiments, respectively. Drought stress reduced tissue water content, leaf dry weight, and chlorophyll fluorescence and increased total carotenoid concentration and electrolyte leakage, and the values of these parameters returned to those of the control levels after rewatering. Reductions in leaf hemicellulose and total plant hemicellulose concentrations and increases in stem and total plant lignin concentrations were observed in Exp. 1; however, LH and TH were not recovered after rewatering. The concentration of leaf acid detergent fiber increased under drought stress and was back to the control level after recovery while leaf neutral detergent fiber remained unchanged under drought stress but decreased after recovery. The transcript levels of CesA1, CesA6, and CesA12 encoding cellulose synthesis and CslHl encoding hemicellulose were suppressed by drought stress but the suppressions were reversed by rewatering. These candidate genes can be used for further studying the mechanisms that regulate cell wall biosynthesis in switchgrass. [ABSTRACT FROM AUTHOR]

Switchgrass (Panicum virgatum L.) is an important feedstock for bioenergy production, but establishment is difficult in cold arid areas. This study determined the conditions required to improve its germination and emergence in the field. Under controlled conditions, the effects of temperature, water status, and light on germination were studied by exposure to 12-h alternating temperatures of 15/5, 20/5, 20/10, 25/10, 35/20, 40/20, and 45/20°C (day/night) and water potentials of 0, -0.2, -0.4, -0.6, -0.8, and -1.2 MPa in culture medium. Maximum percentage germination occurred at 35/20°C, 0 MPa water potential, and in continuous dark. In the field when planted in early spring (April), no emergence occurred when there was no surface cover or covered with straw mulch (SM) whereas using plastic film mulch (FM), emergence reached 383 seedlings m-2 with pre-sowing irrigation but only 273 without irrigation. This was associated with higher soil temperatures and better soil moisture. However, in July seeding, SM lead to better water status and cooler soil conditions and thus better stand establishment. In contrast, FM treatment had poor establishment primarily due to the high temperatures. Our study indicates that emergence of switchgrass in an arid environment was (i) enhanced by pre-sowing irrigation and shallow seeding, (ii) made possible in spring by the use of FM, and (in) improved with SM for summer seeding. [ABSTRACT FROM AUTHOR]