Linkage Maps of Lowland and Upland Tetraploid Switchgrass Ecotypes

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

Breeding for Biomass Yield in Switchgrass Using Surrogate Measures of Yield

Development of switchgrass (Panicum virgatum L.) as a dedicated biomass crop for conversion to energy requires substantial increases in biomass yield. Most efforts to breed for increased biomass yield are based on some form of indirect selection. The objective of this paper is to evaluate and compare the expected efficiency of several indirect measures of breeding value for improving sward-plot biomass yield of switchgrass. Sward-plot biomass yield, row-plot biomass, and spaced-plant biomass were measured on 144 half-sib families or their maternal parents from the WS4U-C2 breeding population of upland switchgrass. Heading date was also scored on row plots and anthesis date was scored on spaced plants. Use of any of these indirect selection criteria was expected to be less efficient than direct selection for biomass yield measured on sward plots, when expressed as genetic gain per year. Combining any of these indirect selection criteria with half-sib family selection for biomass yield resulted in increases in efficiency of 14 to 36%, but this could only be achieved at a very large cost of measuring phenotype on literally thousands of plants that would eventually have no chance of being selected because they were derived from inferior families. Genomic prediction methods offered the best solution to increase breeding efficiency by reducing average cycle time, increasing selection intensity, and placing selection pressure on all additive genetic variance within the population. Use of genomic selection methods is expected to double or triple genetic gains over field-based half-sib family selection.     

Managing Spatial and Temporal Switchgrass Biomass Yield Variability

Biorefineries that plan to use switchgrass exclusively will encounter year-to-year variability in feedstock production. The economic success of the biorefinery will depend in part on the ability of the management team to strategically identify land for conversion from current use to the production of switchgrass enabling a flow of feedstock for the life of the biorefinery. The objective of this research is to determine the optimal quality, quantity, and location of land to lease while considering the spatial and temporal variability of switchgrass biomass yield. A calibrated biophysical simulation model was used to simulate switchgrass biomass yields for 50 years based on historical weather data from 1962 to 2011, for three land capability classes for each of 30 counties. Mathematical programming models were constructed and solved to determine the optimal leasing scheme for each of three strategies for a biorefinery that requires 2,000 Mg/day. As expected, a model based on the assumption that the average yield would be obtained in each year finds that production from land identified for leasing would be insufficient to fulfill the biorefinery’s needs in half of the years. In the absence of other sources of biomass, the feedstock shortage would require forced idling of the biorefinery for an average of 29.5 days during these years. Results of a strategy of leasing sufficient land to cover feedstock needs in the worst year from among 50 years for which data are available are compared to that of a strategy enabling year-to-year storage.     

Biomass Yield and Nutrient Responses of Switchgrass to Phosphorus Application

Increasing desire for renewable energy sources has increased research on biomass energy crops in marginal areas with low potential for food and fiber crop production. In this study, experiments were established on low phosphorus (P) soils in southern Oklahoma, USA to determine switchgrass biomass yield, nutrient concentrations, and nutrient removal responses to P and nitrogen (N) fertilizer application. Four P rates (0, 15, 30, and 45?kg?P?ha^?1) and two N fertilizer rates (0 and 135?kg?N?ha^?1) were evaluated at two locations (Ardmore and Waurika) for 3?years. While P fertilization had no effect on yield at Ardmore, application of 45?kg?P?ha^?1 increased yield at Waurika by 17% from 10.5 to 12.3?Mg?ha^?1. Across P fertilizer rates, N fertilizer application increased yields every year at both locations. In Ardmore, non-N-fertilized switchgrass produced 3.9, 6.7, and 8.8?Mg?ha^?1, and N-fertilized produced 6.6, 15.7, and 16.6?Mg?ha^?1 in 2008, 2009, and 2010, respectively. At Waurika, corresponding yields were 7.9, 8.4, and 12.2?Mg?ha^?1 and 10.0, 12.1, and 15.9?Mg?ha^?1. Applying 45?kg?P?ha^?1 increased biomass N, and P concentration and N, P, potassium, and magnesium removal at both locations. Increased removal of nutrients with N fertilization was due to both increased biomass and biomass nutrient concentrations. In soils of generally low fertility and low plant available P, application of P fertilizer at 45?kg?P?ha^?1 was beneficial for increasing biomass yields. Addition of N fertilizer improves stand establishment and biomass production on low P sites.     

Effect of Nitrogen Fertilization and Residual Nitrogen on Biomass Yield of Switchgrass

Switchgrass, Panicum virgatum L., grown for biomass has been extensively researched where the annual precipitation >760 mm and the climate varies from humid to moist-subhumid. Research is needed for areas that receive <700 mm of precipitation, where the climate varies from dry-subhumid to semiarid. The objectives were to determine (1) the effect of nitrogen fertilization on biomass production, (2) the effect of residual nitrogen on biomass production, (3) the nitrogen yield from harvested biomass, and (4) the concentration of soil organic carbon (SOC) from switchgrass plots. Plots were fertilized annually with nitrogen at the rates of 0, 40, 80, and 120 kg ha^?1 from 2008 to 2011 and unfertilized from 2012 to 2015. The biomass yield varied with N rate × production year interactions (P < 0.05), and biomass yield as a function of N rate was either linear or curvilinear depending upon production year. When fertilized, the biomass yield averaged 4.4, 9.4, 11.6, and 13.2 ± 0.4 Mg ha^?1 for the 0, 40, 80, and 120 kg ha^?1 N rates, respectively. Residual nitrogen sustained high biomass yields for 1 year after fertilization ceased. The nitrogen harvested in biomass varied with N rate × production year interactions (P < 0.05), and the harvested nitrogen yield as a function of N rate was linear each year. Fertilization increased the concentration of SOC an average of 1.0 ± 0.2 mg g^?1 of soil. The data suggest that producers could occasionally skip a year of nitrogen fertilization without detrimentally impacting the production of switchgrass biomass.     

四倍体栽培棉种产量和纤维品质性状的QTL定位

陆地棉和海岛棉是两个不同的四倍体栽培种 ,但在生产上各有其特点 ,陆地棉丰产性强 ,海岛棉纤维品质优良 ,利用其种间杂交群体定位产量和品质性状的QTL ,对于分子标记辅助的海岛棉优质纤维向陆地棉转移很有意义。以SSR和RAPD为分子标记 ,陆地棉与海岛棉杂种 (邯郸 2 0 8×Pima90 )F2 群体为作图群体 ,构建了一张含 12 6个标记的遗传图谱 ,包括 6 8个SSR标记和 5 8个RAPD标记 ,可分为 2 9个连锁群 ,标记间平均距离为 13 7cM ,总长1717 0cM ,覆盖棉花总基因组约 34 34% ;以遗传图 12 6个标记为基础 ,对F2 :3 家系符合正态分布的 10个农艺性状及纤维品质性状进行全基因组QTL扫描 ,结果发现 2 9个QTL分别与产量和品质性状有关。其中与衣指、籽指、皮棉产量、子棉产量、衣分等产量性状相关的QTL分别有 1、3、5、6和 1个 ,与纤维长度、整齐度、强度、伸长率和马克隆值等品质性状相关的QTL分别有 2、4、2、4和 1个。各QTL解释的变异量在 12 4 2 %～ 47 0 1%之间。其中比强度有关的 2个QTL能够解释的表型变异率分别为 34 15 %和 13 86 %。     

Nitrogen-Use Dynamics in Switchgrass Grown for Biomass

This work examines N use by switchgrass (Panicum virgatum L.). A study was conducted on two well-established ‘Cave-in-Rock’ switchgrass stands in Blacksburg (37° 11′ N, 80° 25′ W) and Orange (38° 13′ N, 78° 07′ W) Virginia, USA. Plots were fertilized in 2001 (year 1) with 0, 90, 180, or 270 kg N per hectare. No additional N was applied in 2002 (year 2) and 2003 (year 3), and biomass was harvested in July and November for years 2 and 3 (but only in November of year 1). Root and soil samples were collected in May, July, September, and November each year and analyzed for N. Nitrogen fertilization did not increase yields in 2001 (year 1), but it did provide residual benefits in 2002 (year 2) and 2003 (year 3). Root-N levels at 15 cm depth increased with fertilization, fluctuated seasonally between roots and shoots, and root-N was reduced over the course of the study. With two harvests per year, about 100 kg N hectare per year were removed in biomass, even in plots with no N added—suggesting N already present in the soils (at 15 cm depth) contributed to yields; but the soil mineral-N pools were reduced by the end of year 3. Nitrogen-use efficiency, apparent N recovery, and partial factor productivity were reduced with higher N applications. The data support the notion that biomass production can be achieved with minimal N inputs, but stands must be managed to maintain that N reserve over the long term. There is also a need to quantify the N pool to depths greater than 15 cm in other agro-ecoregions.     

QTL Mapping for Fiber and Yield Traits in Upland Cotton under Multiple Environments

A population of 178 recombinant inbred lines (RILs) was developed using a single seed descendant from a cross between G. hirsutum. acc DH962 and G. hirsutum. cv Jimian5, was used to construct a genetic map and to map QTL for fiber and yield traits. A total of 644 polymorphic loci were used to construct a final genetic map, containing 616 loci and spanning 2016.44 cM, with an average of 3.27 cM between adjacent markers. Statistical analysis revealed that segregation distortion in the intraspecific population was more serious than that in the interspecific population. The RIL population and the two parents were phenotyped under 8 environments (two locations, six years), revealing a total of 134 QTL, including 64 for fiber qualities and 70 for yield components, independently detected in seven environments, explaining 4.40–15.28% of phenotypic variation (PV). Among the 134 QTL, 9 common QTL were detected in more than one environment, and 22 QTL and 19 new QTL were detected in combined analysis (E9). A total of 26 QTL hotspot regions were observed on 13 chromosomes and 2 larger linkage groups, and some QTL clusters related to fiber qualities or yield components were also observed. The results obtained in the present study suggested that to map accurate QTL in crops with larger plant types, such as cotton, phenotyping under multiple environments is necessary to effectively apply the obtained results in molecular marker-assisted selection breeding and QTL cloning.     

Switchgrass Biomass and Nitrogen Yield with Over-Seeded Cool-season Forages in the Southern Great Plains

In dry climates with long, hot summers and freezing winters, such as that of the southern Great Plains of North America, switchgrass (Panicum virgatum L.) has proven potential as a cellulosic bioenergy feedstock. This trial looked at dry matter (DM) and N yield dynamics of switchgrass overseeded with cool-season legumes and rye (Secale cereale L.), compared to switchgrass fertilized with 0, 56 and 112 kg N ha^-1 yr^-1 at an infertile and a fertile location. Optimal N fertilizer rate on switchgrass was 56 kg N ha^-1 at the infertile location. Legume yield was greater in the first season after planting, compared to subsequent years where annual legumes were allowed to reseed and alfalfa (Medicago sativa L.) was allowed to grow. This suggests that the reseeding model for annual legumes will not work in switchgrass swards grown for biomass unless soil seed banks are built up for more than one year, and that overseeding with alfalfa may have to be repeated in subsequent years to build up plant populations. Overseeding rye and legumes generally did not suppress or enhance switchgrass biomass production compared to unfertilized switchgrass. However, cumulative spring and fall biomass yields were generally greater due to winter and spring legume production, which could be beneficial for grazing or soil conservation systems, but not necessarily for once-yearly late autumn harvest biofuel production systems.     

Harvest Date Effects on Biomass Yield,Moisture Content,Mineral Concentration,and Mineral Export in Switchgrass and Native Polycultures Managed for Bioenergy

Various local factors influence the decision of when to harvest grassland biomass for renewable energy including climate, plant composition, and phenological stage. However, research on biomass yield and quality related to a wide range of harvest timing from multiple environments and years is lacking. Our objective was to determine the effect of harvest timing on yield, moisture, and mineral concentration of switchgrass (Panicum virgatum L.) and native polyculture biomass. Biomass was harvested on 56 unique days ranging from late summer (2 September) to late spring (20 May) spanning 3 years (2009 to 2011) and seven sites in Minnesota, USA. Biomass yield varied considerably by location and year (range?=?0.7–11.7 Mg ha^?1) and was lowest during the winter. On average, there was no difference in biomass yield harvested in early fall compared to late spring. Biomass moisture content was lowest in late spring, averaging 156 g kg^?1 across all locations and years when harvested after 1 April. Biomass N concentration did not change across harvest dates; however, P and K concentrations declined dramatically from late summer to late spring. Considering the economic costs of replacing exported minerals and changes in revenues from biomass yield through time, biomass harvest should be conducted in late summer–early fall or late spring and avoided in winter. However, biomass managed for gasification should be harvested in spring to reduce concentrations of minerals that lead to slagging and fouling. Changes in biomass yield and quality through time were similar for switchgrass and native polyculture biomass. These biomass harvest recommendations are made from data spanning multiple years and locations and should be applicable to various growing conditions across the Upper Midwest.     

Spatial and Temporal Effects on Switchgrass Stands and Yield in the Great Plains

Switchgrass (Panicum virgatum L.) is being developed into a perennial, herbaceous, cellulosic feedstock crop for use in temperate regions of the USA. Information on spatial and temporal variation for stands and biomass yield among and within fields in large agroecoregions is not available. Spatial and temporal variation information is needed to model feedstock availability for biorefineries. In this 5-yr study, the spatial and temporal variation for biomass yield and stands was determined among and within 10 fields located in North Dakota, South Dakota, and Nebraska. Switchgrass fields were managed for bioenergy from 2000 to 2004 for the Nebraska locations and 2001 to 2005 for the South Dakota and North Dakota locations. A global positioning system (GPS) receiver was used to repeatedly measure within field quadrat sites for switchgrass stands using frequency grid (2.25 m²) measurements in June for five growing seasons. Sixteen quadrat (≥1 m²) yield samples were taken post-killing frost in the establishment year and in August in subsequent years at each location. Topographic within field effects on switchgrass stand frequency and biomass yields were largely insignificant. Stands tended to increase from establishment year to year 3 and then begin to plateau. Weather factors, which were the principal source of temporal variation, were more important in switchgrass yield variation than on switchgrass stand frequencies. Temporal standard deviations for yield were higher on quadrat sites with higher than average field means while temporal standard deviations were smaller in quadrat sites that had lower than average field means at six locations. In the Northern Great Plains agroecoregion, there is greater temporal and spatial variation for switchgrass biomass yields among fields than within fields. Results indicate that modeling feedstock availability for a biorefinery can be based on field scale yields.     

Biomass Yield and Composition of Switchgrass Bales on Marginal Land as Influenced by Harvest Management Scheme

Switchgrass (Panicum virgatum L.) is well suited to marginal croplands, but is difficult to manage sustainably both for maximum yield and optimal biomass composition. Quality can be improved by overwintering switchgrass in the field, but more information is needed on amount and consistency of yield recovery in spring. Two cultivars of switchgrass were sown on separate fields in Freeville, NY, and mowed and baled in late fall (FALL), mowed in fall and baled in spring (WINTER), or mowed and baled in spring (SPRING), using conventional field harvesting equipment. Samples were collected for analysis of plant morphological components and for determining the influence of harvest stubble height on yield and composition. Recovery of FALL biomass yields the following spring ranged from 52 to 82% and was related to both total winter snowfall and to the spring date when soil was dry enough to allow equipment traffic. Approximately 1% of dry matter yield was left in the field for each centimeter of stubble height following mowing. Bale moisture content was very low in spring, averaging 7.3%, but was much more variable and higher in the fall, averaging 22% for “Cave-in-Rock”. Inflorescence and leaf blade were the primary morphological components lost in standing switchgrass over winter. The SPRING treatment can be mowed and baled on the same day without other field operations and has higher quality than WINTER, with no consistent yield advantage for either spring baling treatment. The large and variable yield loss due to overwintering switchgrass in the field makes the practice questionable.     

Genetic Analysis on Gene Effects and GE Interaction Effects for Kernel Nutrient Quality Traits of Upland Cotton

1IntroductionCanon~,whichhavehighcontentOfoilandprotein,areanimPOrtantnutrientr~eforfaceandforage.~areanewgenerationresultedfromfertilndionOff~eandmalegarnetes,butmOStOfseednutrientSareprovidedbymat~plantSonwhichseedsbeal.Therefore,seedtTaitS~besdriltaneouslyconchedbyednucleargenes,cytOPhangenes,andmaternalplantnucleargenes.SeeddireCteffectsandmaternaleffeCtshavebendetectedforseedquantitativetraitsinsomecrOPssuChasrapeseed(PleinesandFriedt,1989),andbarley(KaePplerandRasmusson,1991).I…     

The Effects of Selection on Linkage Analysis for Quantitative Traits

The effects of within-sample selection on the outcome of analyses detecting linkage between genetic markers and quantitative traits were studied. It was found that selection by truncation for the trait of interest significantly reduces the differences between marker genotype means thus reducing the power to detect linked quantitative trait loci (QTL). The size of this reduction is a function of proportion selected, the magnitude of the QTL effect, recombination rate between the marker locus and the QTL, and the allele frequency of the QTL. Proportion selected was the most influential of these factors on bias, e.g., for an allele substitution effect of one standard deviation unit, selecting the top 80%, 50% or 20% of the population required 2, 6 or 24 times the number of progeny, respectively, to offset the loss of power caused by this selection. The effect on power was approximately linear with respect to the size of gene effect, almost invariant to recombination rate, and a complex function of QTL allele frequency. It was concluded that experimental samples from animal populations which have been subjected to even minor amounts of selection will be inefficient in yielding information on linkage between markers and loci influencing the quantitative trait under selection.     

Identification of Associated SSR Markers for Yield Component and Fiber Quality Traits Based on Frame Map and Upland Cotton Collections

Detecting QTLs (quantitative trait loci) that enhance cotton yield and fiber quality traits and accelerate breeding has been the focus of many cotton breeders. In the present study, 359 SSR (simple sequence repeat) markers were used for the association mapping of 241 Upland cotton collections. A total of 333 markers, representing 733 polymorphic loci, were detected. The average linkage disequilibrium (LD) decay distances were 8.58 cM (r² > 0.1) and 5.76 cM (r² > 0.2). 241 collections were arranged into two subgroups using STRUCTURE software. Mixed linear modeling (MLM) methods (with population structure (Q) and relative kinship matrix (K)) were applied to analyze four phenotypic datasets obtained from four environments (two different locations and two years). Forty-six markers associated with the number of bolls per plant (NB), boll weight (BW), lint percentage (LP), fiber length (FL), fiber strength (FS) and fiber micornaire value (FM) were repeatedly detected in at least two environments. Of 46 associated markers, 32 were identified as new association markers, and 14 had been previously reported in the literature. Nine association markers were near QTLs (at a distance of less than 1–2 LD decay on the reference map) that had been previously described. These results provide new useful markers for marker-assisted selection in breeding programs and new insights for understanding the genetic basis of Upland cotton yields and fiber quality traits at the whole-genome level.     

冬小麦产量性状的遗传效应分析

以农大139等7个冬小麦品种进行4×3不完全双列杂交,采用加性-显性及其与环境互作的遗传模型对亲本、F_1和F_2的株高、主穗穗长、单株穗数、主穗小穗数、千粒重和单株粒重6个性状进行遗传分析．结果表明,株高和主穗长主要受加性效应控制,而单株穗数、主穗小穗数、千粒重和单株粒重主要受显性×环境互作效应影响．矮2杂交后代易选到矮株,奥里生杂交后代易得到大穗材料,农林10号和奥里生的杂交后代分蘖力将加强,814的杂交后代小穗数增多,814杂交后代千粒重增高．所有产量性状未表现明显的杂种优势．     

Yield and Woody Biomass Traits of Novel Shrub Willow Hybrids at Two Contrasting Sites

Shrub willow has great potential as a dedicated bioenergy crop, but commercialization and adoption by growers and end-users will depend upon the identification and selection of high-yielding cultivars with biomass chemistry and quality amenable to conversion to biofuels and bioenergy. In this study, critical traits for biomass production were evaluated among new genotypes of shrub willow produced through hybrid breeding. This study assessed the variation in yield, pest and disease resistance, biomass composition, and wood density in shrub willow, as well as the impact of genotypic and environmental factors on these particular phenotypes. Analysis of clonal genotypes established on two contrasting sites in New York State, Tully and Belleville, showed statistical differences by site for all of the traits. The greatest yield was observed at Belleville, NY, for two cultivars, ‘Fish Creek’ (41 Mg?ha^?1) and ‘Onondaga’ (40 Mg?ha^?1). Yields of Salix eriocephala genotypes were lowest, and they displayed susceptibility to rust and beetle damage. Variation in cellulose content in the stem biomass was controlled by environmental factors, with the majority of the genotypes displaying greater cellulose content at Belleville compared with Tully. In contrast, wood density was significantly greater at Tully than Belleville, and cellulose content was correlated with wood density. There were no significant correlations between biomass yield and density or any of the composition traits. These trials demonstrate that new genotypes produce improved yield and pest and disease resistance, with diverse compositional traits that can be matched with conversion technologies.