William F. Anderson

Structural and chemical properties of grass lignocelluloses related to conversion for biofuels

Grass lignocelluloses, such as those in corn and switchgrass, are a major resource in the emerging cellulose-to-ethanol strategy for biofuels. The potential bioconversion of carbohydrates in this potential resource, however, is limited by the associated aromatic constituents within the grass fiber. These aromatics include both lignins, which are phenylpropanoid units of various types, and low-molecular weight phenolic acids. Structural and chemical studies over the years have identified the location and limitation to fiber degradation imposed by a variety of these aromatic barriers. For example, coniferyl lignin appears to be the most effective limitation to biodegradation, existing in xylem cells of vascular tissues. On the other hand, cell walls with syringyl lignin, e.g., leaf sclerenchyma, are often less recalcitrant. Ferulic and p-coumaric acids that are esterified to hemicellulosic sugars constitute a major limitation to biodegradation in non-lignified cell walls in grass fibers, especially warm season species. Non-chemical methods to improve bioconversion of the lignocelluloses through modification of aromatics include: (1) use of lignin-degrading white rot fungi, (2) pretreatment with phenolic acid esterases, and (3) plant breeding to modify cell wall aromatics. In addition to increased availability of carbohydrates for fermentation, separation and collection of aromatics could provide value-added co-products to improve the economics of bioconversion.

Somatic embryogenesis in Arachis hypogaea L." genotype comparison

Somatic embryogenesis and embryogenic callus formation occurred from immature cotyledon and embryo axis explants of seven peanut (Arachis hypogaea L.) genotypes including one valencia, three Spanish and three Virginia botanical types. The initiation medium consisted of Murashige and Skoogs salts and vitamins with 3% sucrose and 0.5 mg/l picloram. There were significant differences among genotypes for somatic embryo formation, subculture capacity and plant regeneration using a single media sequence. Somatic embryo formation from cotyledons showed better correlation with plant regeneration than somatic embryo formation from the embryo axis. Maturity of the embryo explant, as estimated by cotyledon length, did not show a significant effect on response, but there was a trend toward reduced somatic embryo formation from older cotyledons. Relatively few plants were regenerated from the valencia genotype. All peanut genotypes tested thus far are competent for somatic embryogenesis and in vitro response could probably be improved by media manipulation.

Dedicated Energy Crops and Crop Residues for Bioenergy Feedstocks in the Central and Eastern USA

Dedicated energy crops and crop residues will meet herbaceous feedstock demands for the new bioeconomy in the Central and Eastern USA. Perennial warm-season grasses and corn stover are well-suited to the eastern half of the USA and provide opportunities for expanding agricultural operations in the region. A suite of warm-season grasses and associated management practices have been developed by researchers from the Agricultural Research Service of the US Department of Agriculture (USDA) and collaborators associated with USDA Regional Biomass Research Centers. Second generation biofuel feedstocks provide an opportunity to increase the production of transportation fuels from recently fixed plant carbon rather than from fossil fuels. Although there is no “one-size-fits-all” bioenergy feedstock, crop residues like corn (Zea mays L.) stover are the most readily available bioenergy feedstocks. However, on marginally productive cropland, perennial grasses provide a feedstock supply while enhancing ecosystem services. Twenty-five years of research has demonstrated that perennial grasses like switchgrass (Panicum virgatum L.) are profitable and environmentally sustainable on marginally productive cropland in the western Corn Belt and Southeastern USA.

Genetic relationships among napiergrass ( Pennisetum purpureum Schum.) nursery accessions using AFLP markers

Pennisetum purpureum Schum. (napiergrass) is a perennial grass used for forage especially in South America and Africa. Over the last 30 years, a USDA–ARS nursery containing accessions collected from all over the world has been established in Tifton, Georgia. The study reported here was conducted to assess the molecular genetic variation and genetic relatedness among 89 accessions from the Tifton nursery using amplified fragment length polymorphism markers, morphological data and ploidy level. Using 218 polymorphic markers from eight selective primer combinations, the 89 accessions were clustered into five groups using a principal components analysis and a dendrogram based on Dice similarity estimates and unweighted pair group method with arithmetic average clustering. These five groups include three groups collected from Kenya, a group from Puerto Rico, and accessions derived from the cultivar Merkeron. This research provides the first molecular characterization of the Tifton nursery, displays the relationships between accessions, and provides potential heterotic groups for napiergrass and pearl millet ( Pennisetum glaucum (L.) R. Br.) breeding improvement.

Aspergillus Colonization and Aflatoxin Contamination in Peanut Genotypes with Resistance to Other Fungal Pathogens

Indirect selection tools would be valuable in the development of peanut (Arachis hypogaea) cultivars with resistance to aflatoxin contamination. The objective of this study was to determine whether resistance to other fungi could be used as an indirect selection tool for resistance to colonization of peanut by Aspergillus flavus group fungi or aflatoxin contamination. Nine peanut genotypes with resistance to late leaf spot (Cercosporidium personatum) or white mold (Sclerotium rolfsii) were evaluated for 2 years at Tifton, GA, and Yuma, AZ. Plots were subjected to late-season heat and drought stress. None of the genotypes exhibited less colonization of shells or kernels by A. flavus group fungi than cv. Florunner when tested in Georgia or Arizona. None of the genotypes showed a reduced level of aflatoxin contamination in comparison to Florunner at either location. These results indicate that the mechanisms of resistance to other fungi operating in these genotypes are not effective in providing resistance to colonization by A. flavus group fungi or reducing aflatoxin contamination. Therefore, resistance to these fungi cannot be used as an indirect selection tool for resistance to aflatoxin contamination.

Dedicated Herbaceous Biomass Feedstock Genetics and Development

Biofuels and bio-based products can be produced from a wide variety of herbaceous feedstocks. To supply enough biomass to meet the needs of a new bio-based economy, a suite of dedicated biomass species must be developed to accommodate a range of growing environments throughout the USA. Researchers from the US Department of Agriculture’s Agricultural Research Service (USDA-ARS) and collaborators associated with the USDA Regional Biomass Research Centers have made major progress in understanding the genetics of switchgrass, sorghum, and other grass species and have begun to use this knowledge to develop new cultivars with high yields and appropriate traits for efficient conversion to bio-based products. Plant geneticists and breeders have discovered genes that reduce recalcitrance for biochemical conversion to ethanol and drop-in fuels. Progress has also been made in finding genes that improve production under biotic and abiotic stress from diseases, pests, and climatic variations.

Biomass production of herbaceous energy crops in the United States: field trial results and yield potential maps from the multiyear regional feedstock partnership

Current knowledge of yield potential and best agronomic management practices for perennial bioenergy grasses is primarily derived from small‐scale and short‐term studies, yet these studies inform policy at the national scale. In an effort to learn more about how bioenergy grasses perform across multiple locations and years, the U.S. Department of Energy (US DOE)/Sun Grant Initiative Regional Feedstock Partnership was initiated in 2008. The objectives of the Feedstock Partnership were to (1) provide a wide range of information for feedstock selection (species choice) and management practice options for a variety of regions and (2) develop national maps of potential feedstock yield for each of the herbaceous species evaluated. The Feedstock Partnership expands our previous understanding of the bioenergy potential of switchgrass, Miscanthus, sorghum, energycane, and prairie mixtures on Conservation Reserve Program land by conducting long‐term, replicated trials of each species at diverse environments in the U.S. Trials were initiated between 2008 and 2010 and completed between 2012 and 2015 depending on species. Field‐scale plots were utilized for switchgrass and Conservation Reserve Program trials to use traditional agricultural machinery. This is important as we know that the smaller scale studies often overestimated yield potential of some of these species. Insufficient vegetative propagules of energycane and Miscanthus prohibited farm‐scale trials of these species. The Feedstock Partnership studies also confirmed that environmental differences across years and across sites had a large impact on biomass production. Nitrogen application had variable effects across feedstocks, but some nitrogen fertilizer generally had a positive effect. National yield potential maps were developed using PRISM‐ELM for each species in the Feedstock Partnership. This manuscript, with the accompanying supplemental data, will be useful in making decisions about feedstock selection as well as agronomic practices across a wide region of the country.

Use of winter legumes as banker plants for beneficial insect species in a sorghum and cotton rotation system.

Abstract Use of novel crops for bio-fuel production requires evaluating the potential for sound ecological and economical implementation in a particular region. We examined the pest and generalist beneficial insect species associated with various winter cover crops (including narrowleaf lupin, white vetch, Austrian winter pea, crimson clover, faba bean, and rye) as sources of colonists in 2 subsequent summer crops, sorghum and cotton. Sorghum is a potential cellulosic bio-fuel crop and cotton is commonly grown in the region and could be a viable low-input rotation for biofuel sorghum. Insects were sampled weekly over 3 ys in winter cover plots beginning in early spring and in the later planted crop plots beginning at the 15 cm height stage of the crops and continuing for 3 - 6 wks. Of the predators, coccinellids (Coleoptera: Coccinellidae) dominated and were consistently abundant in vetch, faba and lupin, as was the pea aphid, Acyrthosiphon pisum Harris (Hemiptera: Aphididae) and the aphid parasitoid, Lysiphlebus testaceipes Cresson (Hymenoptera: Aphiidae). Orius spp. (Hemiptera: Anthocoridae) dominated in lupin. Of the pest species, thrips spp. (Thysanoptera: Thipidae) were highest in lupin and pea, and stink bugs (Hemiptera: Pentatomidae) were highest in clover. No differences in chinch bugs (Hemiptera: Lygaeidae) were found among the covers. There was a ‘relay’ of these species into all of the summer crop plots from living winter crops. Boll damage from stink bugs was highest in the cotton following lupin, pea and fallow with fertilizer; there was no damage from chinch bugs in sorghum. Faba beans had declining stands over the 3 ys, suggesting that this species would not be a reliable winter crop in this system. Vetch and lupin may be the best candidates as banker plants because of their ability to consistently sustain pea aphids and coccinellids, the former which is a nonpest of sorghum and cotton.

Chemical Analysis of Fermentable Sugars and Secondary Products in 23 Sweet Sorghum Cultivars

Sorghum (Sorghum bicolor (L.) Moench) is a heat- and drought-tolerant crop that has promise to supplement corn (Zea mays L.) for biofuel production from fermentable sugars (for sweet cultivars) and lignocellulosic biomass. Quantitative relationships are lacking to predict the accumulation of primary (stem sugars) and secondary (organic acids, phenolics, and inorganic species) products that could either expand (as the value-added product) or limit (as the fermentation inhibitor) the market value of a cultivar. Five male (Atlas, Chinese, Dale, Isidomba, N98) and three female (N109B, N110B, and N111B) inbred lines and their hybrids (23 cultivars total) were planted on a Tifton loamy sand in April, May, and June of 2015 in a triplicate split-plot design and were harvested at the hard-dough maturity stage. Stalk juices were analyzed for sugar (glucose, fructose, and sucrose) and organic acid (citrate, oxalate, and cis- and trans-aconitic acid) concentrations, Brix, pH, electric conductivity (EC), total organic carbon (TOC), and total nitrogen (TN), and by fluorescence excitation emission spectrophotometry with parallel factor analysis (EEM/PARAFAC). Later plantings consistently (p < 0.05) (1) increased sucrose, total sugar, and trans-aconitic acid concentrations, Brix, and TOC and (2) decreased EC. Sucrose, total sugar, pH, EC, and Brix showed significant cultivar × planting date interactions. Observed linear relationships (Pearsons) could be used to deploy simple and inexpensive electrode (EC) and fluorescence-based field methods to predict the primary products from secondary products, and vise versa.

Evaluation of Whorl Damage by Fall Armyworm (Lepidoptera: Noctuidae) on Field- and Greenhouse-Grown Sweet Sorghum Plants

Abstract  The fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), is an economically important pest of sorghum, Sorghum bicolor (L.) Moench. However, resistance to fall armyworm in sweet sorghum has not been extensively studied. A collection of primarily sweet sorghum accessions were evaluated in the field for natural fall armyworm infestation. Fall armyworm damage ratings ranged from 1.88 ± 0.35 to 4.75 ± 0.37, suggesting that a range of response to fall armyworm feeding exists in this collection. Based on the results of field data from two planting dates, accessions with the highest and lowest fall armyworm damage ratings were selected for greenhouse evaluations. At 7 d after infestation, the sorghum accessions, excluding BTx623 and Plant Introduction (PI) 147573, had significantly higher fall armyworm damage than resistant control MP708. Furthermore, at 7 d after the infestation, genotype PI 147573 was the most resistant; whereas, genotypes 13, 22, ‘GT-IR8′, and ‘GT-IR6′ were the most susceptible to fall armyworm feeding. For the damage ratings at 14 d after the infestation, sorghum Entry 13 had significantly higher fall armyworm damage than GT-IR7 and PI 17548. At 14 d after infestation, all nine sorghum accessions were as resistant as the MP708 resistant control and had significantly less damage than the susceptible control AB24E. These data suggest that the sorghum lines at 14 d have induced resistance in the growing whorl.