E. Charles Brummer

Biomass yield and quality of 20 switchgrass populations in southern Iowa, USA

Renewable bioenergy could be supplied by high yielding grass crops, such as switchgrass (Panicum virgatum L.). Successful development of a bioenergy industry will depend on identifying cultivars with high yield potential and acceptable biofuel quality. The objective of this study was to evaluate 20 switchgrass populations in a field study planted in May 1997 in southern Iowa, USA. The populations included released cultivars and experimental germplasm of both upland and lowland ecotypes. Yield, plant height, stand, lodging, leaf:stem ratio, cell wall fiber, total plant nitrogen, and ash were determined on all entries between 1998 and 2001. Ultimate and proximate analyses together with chlorine and major oxide determinations were made on three cultivars in 2000 and 2001. Biomass yield was determined from a single autumn harvest each year. The lowland cultivars ‘Alamo’ and ‘Kanlow’ produced the most biomass, exceeding the production of the widely recommended upland cultivar ‘Cave-In-Rock’. Other traits differed among the cultivars, although the range was less than that for yield. The differences among years were substantially greater for the ultimate, proximate, and major oxide analyses than differences among cultivars. The highest yielding cultivars had low ash, slightly lower fiber concentrations, and moderate levels of important minerals, suggesting that excellent germplasm is available for biofuel production. The persistence of the lowland cultivars in southern Iowa may need more research because the winters during the experiment were mild.

Legumes as a Model Plant Family. Genomics for Food and Feed Report of the Cross-Legume Advances through Genomics Conference

On December 14 to 15, 2004, some 50 legume researchers and funding agency representatives (the latter as observers) met in Santa Fe, New Mexico, to develop a plan for cross-legume genomics research. This conference was one of the outcomes of the Legume Crops Genome Initiative (LCGI), an organization

Development of an RFLP map in diploid alfalfa.

SummaryWe have developed a restriction fragment length polymorphism (RFLP) linkage map in diploid alfalfa (Medicago sativa L.) to be used as a tool in alfalfa improvement programs. An F2 mapping population of 86 individuals was produced from a cross between a plant of the W2xiso population (M. sativa ssp. sativa) and a plant from USDA PI440501 (M. sativa ssp. coerulea). The current map contains 108 cDNA markers covering 467.5 centimorgans. The short length of the map is probably due to low recombination in this cross. Marker order may be maintained in other populations even though the distance between clones may change. About 50% of the mapped loci showed segregation distortion, mostly toward excess heterozygotes. This is circumstantial evidence supporting the maximum heterozygote theory which states that relative vigor is dependent on maximizing the number of loci with multiple alleles. The application of the map to tetraploid populations is discussed.

Comparisons of genetic and morphological distance with heterosis between Medicago sativa subsp. sativa and subsp. falcata

Biomass yield heterosis has been shown to exist between Medicago sativasubsp. sativa and Medica gosativa subsp. falcata. The objective of this study was to gain a better understanding of what morphological and genetic factors were most highly correlated with total biomass yield heterosis. We calculated genetic distances among nine sativa and five falcate genotypes based on amplified fragment length polymorphism (AFLP) and simple sequence repeat (SSR) DNA markers. Genetic distance did not correlate with specific combining ability (SCA) or mid-parent heterosis. In contrast, a morphological distance matrix based on seventeen agronomic and forage quality traits was significantly correlated with heterosis; the agronomic traits of maturity, midseason regrowth, and autumn regrowth showed strong association with heterosis. Heterosis was also correlated with subspecies. We suggest that in many cases progeny heterosis can be accounted for by the interaction of genes controlling morphologically divergent traits between the parents. In other cases, progeny heterosis could also be due to divergence between the parents at particular genetic loci that do not control field-level phenotypic differences. Genetic distanceper se between parental genotypes, based on neutral molecular markers, however, does not reflect the potential of individual genotypes to produce heterosis in their progeny.

Chemical Profiles of Switchgrass

Chemical analysis studies were conducted for four populations of switchgrass (Alamo, Kanlow, GA993, and GA992), Panicum virgatum L., which were partitioned into leaves, internodes, and nodes. The variations in carbohydrate compositions, lignin and extractives content, higher heating value (HHV), and the syringyl:guaiacyl ratio of switchgrass were determined. The experimental results indicated that bulk chemical profiles for the four populations of switchgrass were comparable. However, the results from three morphological components of switchgrass, leaves, internodes and nodes, provided a significant diversity among the analytical results studied.

Achievements and Challenges in Improving Temperate Perennial Forage Legumes

The expected move towards more sustainable crop-livestock systems implies wider cultivation of perennial forage legumes. Alfalfa (Medicago sativa subsp. sativa) is the main perennial legume in most temperate regions, especially where farm systems rely largely on forage conservation. White clover (Trifolium repens) and red clover (Trifolium pratense) are dominant in specific regions and farm systems. Although breeding progress for disease and insect resistance has been achieved, these crops have shown lower rates of genetic gain for yield than major grain crops, owing to lower breeding investment, longer selection cycles, impossibility to capitalize on harvest index, outbreeding mating systems associated with severe inbreeding depression, and high interaction of genotypes with cropping conditions and crop utilizations. Increasing yield, persistence, adaptation to stressful conditions (drought; salinity; grazing) and compatibility with companion grasses are major breeding targets. We expect genetic gain for yield and other complex traits to accelerate due to progress in genetic resource utilization, genomics resource development, integration of marker-assisted selection with breeding strategies, and trait engineering. The richness in adaptive genes of landraces and natural populations can be fully exploited through an ecological understanding of plant adaptive responses and improved breeding strategies. Useful genetic variation from secondary and tertiary gene pools of Medicago and Trifolium is being increasingly accessed. Genome sequencing projects in alfalfa and white clover will enrich physical, linkage and trait maps. Genome sequences will underpin fine mapping of useful loci and subsequent allele mining, leveraging the synteny of these crops with M. truncatula. Low-cost genome-wide markers generated through genotyping-by-sequencing will make genomic selection for adaptation and forage yield possible for these crops. Genetic markers will also be used for dissecting quantitative traits and developing toolboxes of functional markers for stress tolerance and other traits. Under current regulatory policies, transgenic approaches are likely to be limited to a few breakthrough traits. The key challenge for future applications of genomics technologies is their seamless integration with breeding system logistics and breeding schemes.

Plant breeding for harmony between agriculture and the environment

Plant breeding programs primarily focus on improving a crops environmental adaptability and biotic stress tolerance in order to increase yield. Crop improvements made since the 1950s – coupled with inexpensive agronomic inputs, such as fertilizers, pesticides, and water – have allowed agricultural production to keep pace with human population growth. Plant breeders, particularly those at public institutions, have an interest in reducing agricultures negative impacts and improving the natural environment to provide or maintain ecosystem services (eg clean soil, water, and air; carbon sequestration), and in creating new agricultural paradigms (eg perennial polycultures). Here, we discuss recent developments in, as well as the goals of, plant breeding, and explain how these may be connected to the specific interests of ecologists and naturalists. Plant breeding can be a powerful tool to bring “harmony” between agriculture and the environment, but partnerships between plant breeders, ecologists, urban plann...

Diverse perennial crop mixtures sustain higher productivity over time based on ecological complementarity

Cropping systems that rely on renewable energy and resources and are based on ecological principles could be more stable and productive into the future than current monoculture systems with serious unintended environmental consequences such as soil erosion and water pollution. In nonagricultural systems, communities with higher species diversity have higher productivity and provide other ecosystem services. However, communities of well-adapted crop species selected for biomass production may respond differently to increasing diversity. Diversity effects may be due to complementarity among species (complementary resource use and facilitative interactions) or positive selection effects (e.g., species with higher productivity dominate the mixture), and these effects may change over time or across environments. Our goal was to identify the ecological mechanisms causing diversity effects in a biodiversity experiment using agriculturally relevant species, and evaluate the implications for the design of sustainable cropping systems. We seeded seven perennial forage species in a replicated field experiment at two locations in Iowa, USA, and evaluated biomass productivity of monocultures and two- to six-species mixtures over 3 years after the establishment year under management systems of contrasting intensity: one or three harvests per year. Productivity increased with seeded species richness in all environments, and the positive relationship did not change over time. Polyculture overyielding was due to complementarity among species in the community rather than to selection effects of individual species. Complementarity increased as a log-linear function of species richness in all environments, and this trend was consistent across years. Legume‐grass facilitation may explain much of this complementarity effect. Although individual species with high biomass production had a major effect on productivity of mixtures, the species producing the highest biomass in monoculture changed over the years in most environments. Furthermore, transgressive overyielding was observed and was more prevalent in later years, in some environments. We conclude that choosing a single well-adapted species for maximizing productivity may not be the best alternative over the long term and that high levels of species diversity should be included in the design of productive and ecologically sound agricultural systems.

Alfalfa Winter Hardiness: A Research Retrospective and Integrated Perspective*

Abstract Insufficient cold hardiness is a major impediment to reliable alfalfa (Medicago sativa L.) production in northern regions experiencing harsh winter conditions. Numerous studies have documented the morphological and physiological traits associated with the acquisition of freezing tolerance and winter survival in alfalfa. Use of this information as selection criteria to breed cultivars with superior winter hardiness has thus far been met with limited success. This can be attributed to many factors including: the large number of traits affecting winter survival; the multigenic nature of most traits, large environmental interactions, and an undesirable linkage between acquisition of freezing tolerance and fall growth cessation (fall dormancy). In the last two decades, the advent of molecular biology and quantitative genetic techniques has markedly increased our knowledge of the molecular and genetic bases of superior alfalfa winter hardiness. Our understanding of the mechanisms underlying the perception of the low temperature signal and its transduction into morphological and physiological responses leading to cold hardiness has progressed, but still remains fragmentary. Current evidence indicates that cold hardiness of alfalfa relies on tolerance to extensive freeze‐induced desiccation. Low temperature‐induced accumulation of soluble sugars and stress‐related translation products were found to be, in some instances, more abundant in cold‐tolerant cultivars and to be under some level of genetic control. Limited stability of these traits and conflicting reports on their relationship with freezing tolerance preclude their adoption as molecular screening tools. The development of robust screening techniques will require a more complete knowledge of the genetic bases of freezing tolerance. Heritability estimates suggest that independent selection for winter hardiness, freezing injury and autumn growth is possible, and that winter hardiness and autumn growth could be manipulated independently. This creates the opportunity to develop high‐yielding cultivars with improved winter hardiness. A screening test for freezing tolerance performed under controlled conditions recently led to the development of populations with increased freezing tolerance and led to significant improvement in alfalfa winter survival. Unique genetic material, combined with novel gene discovery approaches, could be lead to the identification of genetic polymorphisms associated with freezing tolerance in alfalfa and pave the way to marker‐assisted selection. Based on the current knowledge, we propose a conceptual framework for the genetic determination of cold adaptation of alfalfa.

A Saturated Genetic Linkage Map of Autotetraploid Alfalfa (Medicago sativa L.) Developed Using Genotyping-by-Sequencing Is Highly Syntenous with the Medicago truncatula Genome

A genetic linkage map is a valuable tool for quantitative trait locus mapping, map-based gene cloning, comparative mapping, and whole-genome assembly. Alfalfa, one of the most important forage crops in the world, is autotetraploid, allogamous, and highly heterozygous, characteristics that have impeded the construction of a high-density linkage map using traditional genetic marker systems. Using genotyping-by-sequencing (GBS), we constructed low-cost, reasonably high-density linkage maps for both maternal and paternal parental genomes of an autotetraploid alfalfa F1 population. The resulting maps contain 3591 single-nucleotide polymorphism markers on 64 linkage groups across both parents, with an average density of one marker per 1.5 and 1.0 cM for the maternal and paternal haplotype maps, respectively. Chromosome assignments were made based on homology of markers to the M. truncatula genome. Four linkage groups representing the four haplotypes of each alfalfa chromosome were assigned to each of the eight Medicago chromosomes in both the maternal and paternal parents. The alfalfa linkage groups were highly syntenous with M. truncatula, and clearly identified the known translocation between Chromosomes 4 and 8. In addition, a small inversion on Chromosome 1 was identified between M. truncatula and M. sativa. GBS enabled us to develop a saturated linkage map for alfalfa that greatly improved genome coverage relative to previous maps and that will facilitate investigation of genome structure. GBS could be used in breeding populations to accelerate molecular breeding in alfalfa.