Lowland Ecotypes Research Articles

Selection for Biomass Yield in Upland, Lowland, and Hybrid Switchgrass

ABSTRACTSwitchgrass (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.

Categories of Resistance to Greenbug and Yellow Sugarcane Aphid (Hemiptera: Aphididae) in Three Tetraploid Switchgrass Populations

Switchgrass, Panicum virgatum L., has been targeted as a bioenergy feedstock. However, little is currently known of the mechanisms of insect resistance in this species. Here, two no-choice studies were performed to determine the categories (antibiosis and tolerance) and relative levels of resistance of three switchgrass populations (Kanlow–lowland ecotype, Summer–upland ecotype, and third generation derivatives between Kanlow × Summer plants, K×S) previously identified with differential levels of resistance to the greenbug, Schizaphis graminum (Rondani), and yellow sugarcane aphid, Sipha flava (Forbes). No-choice studies indicated that Kanlow possessed multi-species resistance, with high levels of antibiosis to both aphid species, based on aphid survival at 7 and 14 days after aphid introduction and cumulative aphid days, while K×S possessed low-to-moderate levels of antibiosis to S. flava. Further, functional plant loss indices based on plant height and biomass indicated that tolerance is an important category of resistance for Summer plants to S. graminum. These studies also indicated that Summer lacks both tolerance and antibiosis to S. flava, relative to the other switchgrasses tested, whereas K×S lack tolerance and antibiosis to S. graminum. These studies are the first attempt to analyze the categories of resistance in switchgrass and provide critical information for characterizing the biological mechanisms of resistance and improving our knowledge of the plant–insect interactions within this system.

Switchgrass cultivar/ecotype selection and management for biofuels in the upper southeast USA.

Switchgrass (Panicum virgatum L.), a perennial warm-season grass indigenous to the eastern USA, has potential as a biofuels feedstock. The objective of this study was to investigate the performance of upland and lowland switchgrass cultivars under different environments and management treatments. Four cultivars of switchgrass were evaluated from 2000 to 2001 under two management regimes in plots established in 1992 at eight locations in the upper southeastern USA. Two management treatments included 1) a single annual harvest (in late October to early November) and a single application of 50 kg N/ha/yr and 2) two annual harvests (in midsummer and November) and a split application of 100 kg N/ha/yr. Biomass yields averaged 15 Mg/ha/yr and ranged from 10 to 22 Mg/ha/yr across cultivars, managements, locations, and years. There was no yield advantage in taking two harvests of the lowland cultivars (Alamo and Kanlow). When harvested twice, upland cultivars (Cave-in-Rock and Shelter) provided yields equivalent to the lowland ecotypes. Tiller density was 36% lower in stands cutting only once per year, but the stands appeared vigorous after nine years of such management. Lowland cultivars and a one-cutting management (after the tops have senesced) using low rates of applied N (50 kg/ha) are recommended.

Production of Autopolyploid Lowland Switchgrass Lines Through In Vitro Chromosome Doubling

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

Natural selection and neutral evolution jointly drive population divergence between alpine and lowland ecotypes of the allopolyploid plant Anemone multifida (Ranunculaceae).

Population differentiation can be driven in large part by natural selection, but selectively neutral evolution can play a prominent role in shaping patters of population divergence. The decomposition of the evolutionary history of populations into the relative effects of natural selection and selectively neutral evolution enables an understanding of the causes of population divergence and adaptation. In this study, we examined heterogeneous genomic divergence between alpine and lowland ecotypes of the allopolyploid plant, Anemone multifida. Using peak height and dominant AFLP data, we quantified population differentiation at non-outlier (neutral) and outlier loci to determine the potential contribution of natural selection and selectively neutral evolution to population divergence. We found 13 candidate loci, corresponding to 2.7% of loci, with signatures of divergent natural selection between alpine and lowland populations and between alpine populations (Fst = 0.074–0.445 at outlier loci), but neutral population differentiation was also evident between alpine populations (FST = 0.041–0.095 at neutral loci). By examining population structure at both neutral and outlier loci, we determined that the combined effects of selection and neutral evolution are associated with the divergence of alpine populations, which may be linked to extreme abiotic conditions and isolation between alpine sites. The presence of outlier levels of genetic variation in structured populations underscores the importance of separately analyzing neutral and outlier loci to infer the relative role of divergent natural selection and neutral evolution in population divergence.

Conversion of switchgrass to ethanol using dilute ammonium hydroxide pretreatment: influence of ecotype and harvest maturity

Switchgrass (Panicum virgatum L.) is a perennial C4 grass that is being developed as a bioenergy crop because it has high production yields and suitable agronomic traits. Five switchgrass biomass samples from upland and lowland switchgrass ecotypes harvested at different stages or maturity were used in this study. Switchgrass samples contained 317.0–385.0 g glucans/kg switchgrass dry basis (db) and 579.3–660.2 g total structural carbohydrates/kg switchgrass, db. Carbohydrate contents were greater for the upland ecotype versus lowland ecotype and increased with harvest maturity. Pretreatment of switchgrass with dilute ammonium hydroxide (8% w/w ammonium loading) at 170°C for 20 min was determined to be effective for preparing switchgrass for enzymatic conversion to monosaccharides; glucose recoveries were 66.9–90.5% and xylose recoveries 60.1–84.2% of maximum and decreased with increased maturity at harvest. Subsequently, pretreated switchgrass samples were converted to ethanol by simultaneous saccharification and fermentation using engineered xylose-fermenting Saccharomyces cerevisiae strain YRH400. Ethanol yields were 176.2–202.0 l/Mg of switchgrass (db) and followed a similar trend as observed for enzymatic sugar yields.

Effects of ecotypes and morphotypes in feedstock composition of switchgrass (Panicum virgatum L.)

AbstractSwitchgrass (Panicum virgatum L.) is a C4 grass with high biomass yield potential and is now a model species for the Bioenergy Feedstock Development Program. Two distinct ecotypes (e.g., upland and lowland) and a range of plant morphotypes (e.g., leafy and stemmy) have been observed in switchgrass. The objective of this study was to determine the influence of ecotype and morphotype on biomass feedstock quality. Leaf and stem tissues of leafy and stemmy morphotypes from both lowland and upland ecotypes were analyzed for key feedstock traits. The leaf : stem ratio of leafy morphotype was more than 40% higher than the stemmy morphotype in both upland and lowland ecotypes. Therefore, the stemmy morphotype has significant advantages over leafy morphotype during harvesting, storage, transportation and finally the feedstock quality. Remarkable differences in feedstock quality and mineral composition were observed in switchgrass genotypes with distinct ecotypic origins and variable plant morphotypes. Lignin, hemicelluloses and cellulose concentrations were higher in stems than in the leaves, while ash content was notably high in leaves. A higher concentration of potassium was found in the stems compared to the leaves. In contrast, calcium was higher and magnesium was generally higher in the leaves compared to stems. The upland genotypes demonstrated considerably higher lignin (14.4%) compared with lowland genotypes (12.4%), while hemicellulose was higher in lowland compared with upland. The stemmy type demonstrated slightly higher lignin compared with leafy types (P < 0.1). Differences between the ecotypes and morphotypes for key quality traits demonstrated the potential for improving feedstock composition of switchgrass through selection in breeding programs.

First Report of Puccinia emaculata Infection on Switchgrass in Virginia.

During the spring of 2007, approximately 2,000 switchgrass plants, representing 168 core switchgrass germplasm, were established in a field nursery at the Virginia Tech Kentland Farm Research Center in Montgomery County, VA. These germplasms were originally obtained from the USDA Plant Genetic Resources Conservation Unit (Griffin, GA) and included both lowland and upland ecotypes. After planting, the switchgrass plants were allowed to establish for 3 years. In the summers of 2009, 2010, and 2011, a substantial infection of a foliar rust pathogen was observed on more than 90% of switchgrass lines in the field. The infected leaves had dark brown pustules that were arranged in a linear fashion between the veins and mainly located on the adaxial surface of the leaf. We observed the infected leaf samples under a microscope and isolated the urediniospores. The urediniospores were brown, round, and averaged 26.08 ± 1.67 μm long and 24.65 ± 1.66 μm wide. Teliospores were observed late in the summers of 2009 and 2010. The teliospores were two-celled, oblong to ellipsoid in shape, and averaged 32.23 ± 3.07 μm in length. The apical cell width averaged 17.6 ± 1.83 μm and the basal cell width averaged 15.08 ± 1.75 μm. The morphology of both the urediniospores and teliospores were similar to Puccinia emaculata Schw. (P. emaculata) (2,3). Using previously established rust disease scoring methods (1), the infected switchgrass lines were evaluated and scored for infection severity on a 0 to 9 scale based on the percentage of leaf area infected, with 0 being either highly resistant or escaping infection and 9 being highly susceptible. The majority of upland switchgrass cultivars, including Caddo, Cave-in-rock, Blackwell, Sunburst, Pathfinder, and Dacotah, were moderately to highly susceptible to this rust pathogen and on average, scored between 7 and 8. However, the majority of lowland switchgrass cultivars, including Alamo, Kanlow, TEM-SEC, TEM-SLC, and TEM-LoDorm, were moderately to highly resistant and scored on average between 3 and 4. This result is consistent with previous reports that show that lowland ecotypes are more resistant to rust diseases (1). To further validate the identity of the rust pathogen, we designed two primers (5'-CCAGTAACGGCGAGTGAAGAG-3' and 5'-CGACTTCCATGGCCACCGTGCGGCTGTCT-3') based on the 18S rDNA sequence of P. emaculata (3). DNA was extracted from bulk infected leaf material for PCR amplification. The 1.2 kb PCR product was isolated and sent for DNA sequencing. The DNA sequence was 98% identical to the 18S rDNA sequence of P. emaculata (EU915294.1). To our knowledge, this study represents the first report of rust on a wide range of various switchgrass cultivars in Virginia.

Bioenergy Traits of Ten Switchgrass Populations Grown in the Northeastern/Mid-Atlantic USA

Although switchgrass (Panicum virgatum L.) has emerged as a bioenergy crop throughout the midwestern and southern USA, little evaluation has been conducted on the performance of switchgrass as a bioenergy crop in the Northeast/Mid-Atlantic. The objectives of this study were to evaluate biomass characteristics of ten switchgrass populations grown in New Jersey and to determine which populations are best for use in biomass production. Ten populations of switchgrass were planted in a spaced-plant nursery in Freehold, NJ and evaluated for: winter injury, anthracnose disease caused by Colletotrichum navitas, lodging, tiller density, height, heading and anthesis date, and biomass yield as well as cellulose, hemicellulose, lignin, ash, chlorine, calcium, magnesium, phosphorous, and potassium in 2007 and 2008. Eastern upland populations 9064202 (Cape May Plant Materials Center accession #9064202), High Tide, and Carthage showed the least amount of winter injury, while southern lowland populations Alamo and Cimarron showed the most winter injury. Lowland populations were less susceptible to anthracnose than upland ecotypes and were taller and later maturing with higher cellulose contents. Lowland populations NSL, Cimarron, and Timber showed the least amount of lodging, and upland populations had the highest tiller densities. Lowland populations Cimarron and Timber had the highest biomass yields of 906.9 and 803.6 kg dry matter plant−1, respectively. Lignocellulosic and mineral contents did not differ greatly among cultivars and generally did not show trends with respect to cytotype. Timber, an eastern lowland ecotype, exhibited the best combination of characteristics and is a promising population for biomass production in the Northeast/Mid-Atlantic region of the USA.

SNP Discovery with EST and NextGen Sequencing in Switchgrass (Panicum virgatum L.)

Although yield trials for switchgrass (Panicum virgatum L.), a potentially high value biofuel feedstock crop, are currently underway throughout North America, the genetic tools for crop improvement in this species are still in the early stages of development. Identification of high-density molecular markers, such as single nucleotide polymorphisms (SNPs), that are amenable to high-throughput genotyping approaches, is the first step in a quantitative genetics study of this model biofuel crop species. We generated and sequenced expressed sequence tag (EST) libraries from thirteen diverse switchgrass cultivars representing both upland and lowland ecotypes, as well as tetraploid and octoploid genomes. We followed this with reduced genomic library preparation and massively parallel sequencing of the same samples using the Illumina Genome Analyzer technology platform. EST libraries were used to generate unigene clusters and establish a gene-space reference sequence, thus providing a framework for assembly of the short sequence reads. SNPs were identified utilizing these scaffolds. We used a custom software program for alignment and SNP detection and identified over 149,000 SNPs across the 13 short-read sequencing libraries (SRSLs). Approximately 25,000 additional SNPs were identified from the entire EST collection available for the species. This sequencing effort generated data that are suitable for marker development and for estimation of population genetic parameters, such as nucleotide diversity and linkage disequilibrium. Based on these data, we assessed the feasibility of genome wide association mapping and genomic selection applications in switchgrass. Overall, the SNP markers discovered in this study will help facilitate quantitative genetics experiments and greatly enhance breeding efforts that target improvement of key biofuel traits and development of new switchgrass cultivars.

Karyotype variation is indicative of subgenomic and ecotypic differentiation in switchgrass

BackgroundKaryotypes can provide information about taxonomic relationships, genetic aberrations, and the evolutionary origins of species. However, differentiation of the tiny chromosomes of switchgrass (Panicum virgatum L.) and creation of a standard karyotype for this bioenergy crop has not been accomplished due to lack of distinguishing features and polyploidy.ResultsA cytogenetic study was conducted on a dihaploid individual (2n = 2X = 18) of switchgrass to establish a chromosome karyotype. Size differences, condensation patterns, and arm-length ratios were used as identifying features and fluorescence in-situ hybridization (FISH) assigned 5S and 45S rDNA loci to chromosomes 7 and 2 respectively. Both a maize CentC and a native switchgrass centromeric repeat (PviCentC) that shared 73% sequence identity demonstrated a strong signal on chromosome 3. However, only the PviCentC probe labeled the centromeres of all chromosomes. Unexpected PviCentC and 5S rDNA hybidization patterns were consistent with severe reduction or total deletion of these repeats in one subgenome. These patterns were maintained in tetraploid and octoploid individuals. The 45S rDNA repeat produced the expected number of loci in dihaploid, tetraploid and octoploid individuals. Differences observed at the 5S rDNA loci between the upland and lowland ecotypes of switchgrass provided a basis for distinguishing these subpopulations.ConclusionCollectively, these results provide a quantitative karyotype of switchgrass chromosomes. FISH analyses indicate genetic divergence between subgenomes and allow for the classification of switchgrass plants belonging to divergent genetic pools. Furthermore, the karyotype structure and cytogenetic analysis of switchgrass provides a framework for future genetic and genomic studies.

Natural Hybrids and Gene Flow between Upland and Lowland Switchgrass

ABSTRACTSwitchgrass (Panicum virgatum L.) is a perennial grass native to the North American tallgrass prairie and savanna habitats and is broadly adapted to the central and eastern United States. Upland and lowland ecotypes represent the two major taxa within switchgrass, which have distinct but overlapping distributions. The purpose of this study was to survey a broad array of putative upland and lowland accessions for the possible presence of natural hybrids or hybrid derivatives and evidence of historic gene flow between the two ecotypes. All plants were classified as upland, lowland, or intermediate based on visual assessment of phenotype, using large nurseries of known upland or lowland plants as controls. A total of 480 plants were surveyed for 19 simple sequence repeat (SSR) markers and sequenced using five chloroplast DNA (cpDNA) segments. Genetic structure analysis revealed 21 individuals with strong evidence for intertaxa hybrid origin and another 25 individuals with moderate evidence for intertaxa hybrid origin. All but two of these individuals originated from remnant populations of the central or eastern Gulf Coast or along the Atlantic Seaboard, a region that is populated with significant quantities of both upland and lowland ecotypes. We propose the central and eastern Gulf Coast glacial refuge as the primary center of origin and diversity for switchgrass, with the western Gulf Coast as the secondary center of origin and diversity. Much of this diversity appears to have been preserved along one of the major northward postglacial migration routes, the Atlantic Seaboard.

Chloroplast Genome Variation in Upland and Lowland Switchgrass

Switchgrass (Panicum virgatum L.) exists at multiple ploidies and two phenotypically distinct ecotypes. To facilitate interploidal comparisons and to understand the extent of sequence variation within existing breeding pools, two complete switchgrass chloroplast genomes were sequenced from individuals representative of the upland and lowland ecotypes. The results demonstrated a very high degree of conservation in gene content and order with other sequenced plastid genomes. The lowland ecotype reference sequence (Kanlow Lin1) was 139,677 base pairs while the upland sequence (Summer Lin2) was 139,619 base pairs. Alignments between the lowland reference sequence and short-read sequence data from existing sequence datasets identified as either upland or lowland confirmed known polymorphisms and indicated the presence of other differences. Insertions and deletions principally occurred near stretches of homopolymer simple sequence repeats in intergenic regions while most Single Nucleotide Polymorphisms (SNPs) occurred in intergenic regions and introns within the single copy portions of the genome. The polymorphism rate between upland and lowland switchgrass ecotypes was found to be similar to rates reported between chloroplast genomes of indica and japonica subspecies of rice which were believed to have diverged 0.2–0.4 million years ago.

Hierarchical classification of switchgrass genotypes using SSR and chloroplast sequences: ecotypes, ploidies, gene pools, and cultivars

Switchgrass (Panicum virgatum L.) is an important crop for bioenergy feedstock development. Switchgrass has two main ecotypes: the lowland ecotype being exclusively tetraploid (2n = 4x = 36) and the upland ecotype being mainly tetraploid and octaploid (2n = 8x = 72). Because there is a significant difference in ploidy, morphology, growth pattern, and zone of adaptation between and within the upland and lowland ecotypes, it is important to discriminate switchgrass plants belonging to different genetic pools. We used 55 simple sequence repeats (SSR) loci and six chloroplast sequences to identify patterns of variation between and within 18 switchgrass cultivars representing seven lowland and 11 upland cultivars from different geographic regions and of varying ploidy levels. We report consistent discrimination of switchgrass cultivars into ecotype membership and demonstrate unambiguous molecular differentiation among switchgrass ploidy levels using genetic markers. Also, SSR and chloroplast markers identified genetic pools related to the geographic origin of the 18 cultivars with respect to ecotype, ploidy, and geographical, and cultivar sources. SSR loci were highly informative for cultivar fingerprinting and to classify plants of unknown origin. This classification system is the first step toward developing switchgrass complementary gene pools that can be expected to provide a significant heterotic increase in biomass yield.

Empirical geographic modeling of switchgrass yields in the United States

AbstractSwitchgrass (Panicum virgatum L.) is a perennial grass native to the United States that has been studied as a sustainable source of biomass fuel. Although many field‐scale studies have examined the potential of this grass as a bioenergy crop, these studies have not been integrated. In this study, we present an empirical model for switchgrass yield and use this model to predict yield for the conterminous United States. We added environmental covariates to assembled yield data from field trials based on geographic location. We developed empirical models based on these data. The resulting empirical models, which account for spatial autocorrelation in the field data, provide the ability to estimate yield from factors associated with climate, soils, and management for both lowland and upland varieties of switchgrass. Yields of both ecotypes showed quadratic responses to temperature, increased with precipitation and minimum winter temperature, and decreased with stand age. Only the upland ecotype showed a positive response to our index of soil wetness and only the lowland ecotype showed a positive response to fertilizer. We view this empirical modeling effort, not as an alternative to mechanistic plant‐growth modeling, but rather as a first step in the process of functional validation that will compare patterns produced by the models with those found in data. For the upland variety, the correlation between measured yields and yields predicted by empirical models was 0.62 for the training subset and 0.58 for the test subset. For the lowland variety, the correlation was 0.46 for the training subset and 0.19 for the test subset. Because considerable variation in yield remains unexplained, it will be important in the future to characterize spatial and local sources of uncertainty associated with empirical yield estimates.

Biomass Production in Switchgrass across the United States: Database Description and Determinants of Yield

Fundamental to deriving a sustainable supply of cellulosic feedstock for an emerging biofuels industry is understanding how biomass yield varies as a function of crop management, climate, and soils. Here we focus on the perennial switchgrass (Panicum virgatum L.) and compile a database that contains 1190 observations of yield from 39 field trials conducted across the United States. Data include site location, stand age, plot size, cultivar, crop management, biomass yield, temperature, precipitation, and information on land quality. Statistical analysis revealed the major sources of variation in yield. Frequency distributions of yield for upland and lowland ecotypes were unimodal, with mean (±SD) biomass yields of 8.7 ± 4.2 and 12.9 ± 5.9 Mg ha−1 for the two ecotypes, respectively. We looked for, but did not find, bias toward higher yields associated with small plots or preferential establishment of stands on high quality lands. A parametric yield model was fit to the data and accounted for one‐third of the total observed variation in biomass yields, with an equal contribution of growing season precipitation, annual temperature, N fertilization, and ecotype. The model was used to predict yield across the continental United States. Mapped output was consistent with the natural range of switchgrass and, as expected, yields were shown to be limited by precipitation west of the Great Plains. Future studies should extend the geographic distribution of field trials and thus improve our understanding of biomass production as a function of soil, climate, and crop management for promising biofuels such as switchgrass.

Natural Variation for Nutrient Use and Remobilization Efficiencies in Switchgrass

Nutrient management in biomass production systems serves to maximize yield and minimize production costs and environmental impact. Loss of soil nutrients with harvested biomass can be reduced by the judicious choice of genotype and harvest time. Sustainable production of switchgrass for biofuel will depend, in part, on breeding of varieties that are conservative in their use of soil nutrients to produce biomass. To aid such breeding programs, we assessed the natural variation in nutrient-use and remobilization efficiencies of 31 accessions of Panicum virgatum by measuring the concentration of 20 elements (N, P, K, Li, B, Na, Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Rb, Sr, Mo, and Cd) in shoots of field-grown plants harvested at two different stages of development. Significant differences between accessions were found for elemental composition at maturity and after senescence. The concentration of several elements (N, P, K, and Rb) decreased in the shoots of all accessions during senescence, although the efficiency of remobilization ranged from 20% to 61% for N, 31% to 65% for P, 25% for 84% for K, and 33% to 84% for Rb. The accessions/cultivars with the greatest nutrient-use efficiency (smallest loss of nutrient per unit biomass) were BN-14668-65, Kanlow, Caddo from the point of view of N content, and Kanlow, Cave-in-Rock, and Blackwell from the point of view of P content in senescent shoots. Finally, differences in elemental composition between upland and lowland ecotypes were also found. The information presented here will help to guide future breeding programs and nutrient management practices.

Tolerance of switchgrass to extreme soil moisture stress: Ecological implications

Switchgrass ( Panicum virgatum L.), a native of eastern and central North America, is a leading candidate as a dedicated biofuel feedstock in the US due to its broad adaptability, rapid growth rate, and ability to grow in low production soils. To begin to characterize the important agronomic and ecological traits related to environmental tolerance of switchgrass, we evaluated fitness under stressful growing conditions. We assessed the germination, establishment, performance, and reproductive potential of four common accessions, both upland and lowland ecotypes, at various levels of soil moisture availability (moisture deficit to flooded) in the greenhouse. Seeds emerged and established (55–90% survival) under all soil moisture conditions (−0.3 MPa to flooded). Transplants of lowland ecotypes performed as well in flooded conditions as in field capacity controls, though flooding reduced performance of upland ecotypes. Drought treatments (−4.0 and −11.0 MPa) reduced tiller length and number, leaf area, and biomass production by up to 80%. However, once established, all plants survived at −4.0 MPa and had the same proportion of tillers in flower as at field capacity. The ability of switchgrass to germinate, establish, and flower in low moisture and flooded conditions, particularly lowland ecotypes, may increase the range of environments suitable for biofuel cultivation, and can serve as a baseline for further ecological studies and genetic improvement.

Adaptation to flooding in upland and lowland ecotypes of Cyperus rotundus, a troublesome sedge weed of rice: tuber morphology and carbohydrate metabolism.

In recent years, Cyperus rotundus has become a problem weed in lowland rice (Oryza sativa) grown in rotation with vegetables in the Philippines. As the growth of C. rotundus is commonly suppressed by prolonged flooding, the ability of the weed to grow vigorously in flooded as well as upland conditions suggests that adapted ecotypes occur in these rotations. Studies were conducted to elucidate the mechanisms that permit C. rotundus to tolerate flooded soil conditions. Upland and lowland ecotypes of C. rotundus were compared in terms of growth habit, carbohydrate reserves and metabolism, and activities of enzymes involved in alcoholic fermentation - alcohol dehydrogenase (ADH) and pyruvate decarboxylase (PDC). The lowland ecotype has much larger tubers than the upland ecotype. Prior to germination, the amylase activity and total non-structural carbohydrate content in the form of soluble sugars were greater in the tubers of lowland plants than in those of upland C. rotundus. At 24 h after germination in hypoxic conditions, PDC and ADH activities in the lowland plants increased, before decreasing at 48 h following germination. In contrast, ADH and PDC activities in the upland plants increased from 24 to 48 h after germination. Tolerance of lowland C. rotundus of flooding may be attributed to large carbohydrate content and amylase activity, and the ability to maintain high levels of soluble sugars in the tubers during germination and early growth. This is coupled with the modulation of ADH and PDC activities during germination, possibly to control the use of carbohydrate reserves and sustain substrate supply in order to avoid starvation and death of seedlings with prolonged flooding.

Molecular and cytological characterization of ribosomal RNA genes inChenopodium quinoaandChenopodium berlandieri

The nucleolus organizer region (NOR) and 5S ribosomal RNA (rRNA) genes are valuable as chromosome landmarks and in evolutionary studies. The NOR intergenic spacers (IGS) and 5S rRNA nontranscribed spacers (NTS) were PCR-amplified and sequenced from 5 cultivars of the Andean grain crop quinoa (Chenopodium quinoa Willd., 2n = 4x = 36) and a related wild ancestor (C. berlandieri Moq. subsp. zschackei (Murr) A. Zobel, 2n = 4x = 36). Length heterogeneity observed in the IGS resulted from copy number difference in subrepeat elements, small re arrangements, and species-specific indels, though the general sequence composition of the 2 species was highly similar. Fifteen of the 41 sequence polymorphisms identified among the C. quinoa lines were synapomorphic and clearly differentiated the highland and lowland ecotypes. Analysis of the NTS sequences revealed 2 basic NTS sequence classes that likely originated from the 2 allopolyploid subgenomes of C. quinoa. Fluorescence in situ hybridization (FISH) analysis showed that C. quinoa possesses an interstitial and a terminal pair of 5S rRNA loci and only 1 pair of NOR, suggesting a reduction in the number of rRNA loci during the evolution of this species. C. berlandieri exhibited variation in both NOR and 5S rRNA loci without changes in ploidy.