Location: Plant Science Research2012 Annual Report
1a. Objectives (from AD-416):
Objective 1: Develop germplasm and determine genetic and biological processes that regulate forage use for bioenergy and livestock production. Sub-objective 1.1. Identify genes and breeding strategies to be used for alfalfa improvement. Sub-objective 1.2. Improve energy availability from forages by modifying genetic, metabolic, and developmental processes that control cell wall synthesis and breakdown. Sub-objective 1.3. Identify and utilize mechanisms to improve nutrient uptake in Medicago spp. Objective 2: Develop and evaluate crop management strategies to increase use of perennial forages for livestock and bioenergy, and to protect the environment. Sub-objective 2.1. Develop management practices and systems to optimize alfalfa composition and biomass yield for the efficient production of liquid fuels and syngas. Sub-objective 2.2. Evaluate strategies to reduce root and foliar disease in alfalfa. Sub-objective 2.3. Develop and test management strategies to expand the role of alfalfa and other perennial forages in protecting water quality.
1b. Approach (from AD-416):
Alfalfa is the backbone of sustainable practices for producing crops and animals while protecting water and soil resources. However, use of alfalfa is not always maximized due to several limitations, and new germplasm and management systems are needed for biofuel production. The objectives of this project are to: (1) develop germplasm and determine genetic and biological processes that regulate forage use for bioenergy and livestock production, and (2) develop and evaluate crop management strategies to increase use of perennial forages for livestock and bioenergy, and to protect the environment. Alfalfa germplasm with greater stem in vitro neutral detergent fiber digestibility (IVNDFD) will be developed through selection and breeding utilizing near-infrared reflectance spectroscopy. Populations will be assessed for changes in cell wall chemistry and biofuel conversion under conventional and biomass management systems. Breeding strategies will be evaluated to increase yield potential. Yield will be evaluated in replicated field trials in multiple locations. Populations with highest yield will be evaluated for total forage yield under conventional and biomass management systems. Management methods for reducing diseases that impact yield and persistence will be assessed. The effect of glyphosate on foliar diseases (rust, powdery mildew, anthracnose, spring black stem) will be evaluated in Roundup Ready alfalfa. Alfalfa cultivars will be screened for resistance to brown root rot and the role of crop debris in pathogen survival and increase will be measured. The potential for green manures and traffic tolerance to reduce crown rot will be evaluated. Genes for disease resistance, cell wall biosynthesis, and nutrient uptake will be isolated to provide new knowledge on the genetic underpinnings of these traits and markers for plant improvement. Transcript profiling will be done to identify candidate genes involved in these traits. The function of specific genes will be investigated through detailed transcript expression studies, investigating promoter activity, biochemical assays, over-expression, and gene knock down. Alfalfa germplasm with greater capacity to remove soil nitrate will be developed by recurrent selection using bromide as a nitrate analog. Populations will be evaluated in multiple field locations for bromide and nitrate uptake. Removal of nitrogen from soil by alfalfa will be tested at the field scale in replicated plots in multiple locations. Forage samples will be analyzed for dry matter and N yield; topsoil will be measured for total N and C. Removal of nitrate from irrigation water via phytofiltration will be tested on a field scale. Replicated plots will be irrigated at normal, high, and intermediate rates and the total nitrate leached determined. Biocurtain strips along tile drainage sites will be managed using conventional and biomass systems along side a corn-soybean rotation. Inorganic N will be measured throughout the growing season in tile drainage water. Fulfilling the objectives will help meet the emerging needs of the nation in livestock and bioenergy production and environmental protection.
3. Progress Report:
Progress was made in developing germplasm and determining genetic and biological processes that regulate forage use for bioenergy and livestock production. From a population selected for forage digestibility, all samples from trials at two locations were analyzed for differences in livestock digestibility and potential ethanol production. Final samples were collected from field experiments comparing alfalfa populations for difference in nitrogen (N) uptake capacity. Gene promoters of novel disease resistance genes were cloned and fused to the GUS marker gene. cDNAs were cloned into vectors for constitutive over-expression. Gene expression and disease resistance is being evaluated in transgenic alfalfa plants. Arabidopsis lines with mutations in the gene homologs were identified and homozygous lines isolated. Testing of disease resistance in Arabidopsis is in progress. Methods for inoculating barrel medic plants with the bacterial wilt pathogen were developed and resistant germplasm identified to facilitate identification of disease resistance genes. Diversity in the pathogen was assessed by rep-PCR (polymerase chain reaction) DNA fingerprinting. The relationship between stem anatomy and cell wall composition was examined in two alfalfa clonal lines that differ in the amount of cellulose and lignin in stem cell walls. Histochemical staining of stem cross-sections revealed that one line exhibited a higher proportion of pith and a lower proportion of secondary xylem consistent with lower amounts of cellulose and lignin in stem cell walls. Progress was made on developing and testing management practices to expand the role of alfalfa for protecting water quality. Field evaluations are in progress in five locations to assess the effect of the fungicide Headline on foliar disease incidence, forage yield, and forage quality. The level of fungicide resistance in the predominant fungal pathogen populations is being tested. A PCR method was developed for amplifying DNA from mycorrhizal fungi, and species associated with alfalfa roots under deficient and sufficient phosphorus conditions were identified. Research on fertilizer N requirements of first-year corn after alfalfa was completed on 15 Minnesota and Wisconsin farms. No response to grain yield was found when corn was planted no-till after alfalfa, consistent with results on fields with full-width tillage. Thus, farmers can save fertilizer, fuel, and carbon emissions and can preserve high yields by reducing tillage after alfalfa. On a separate set of nine on-farm sites, livestock manure applied when alfalfa was terminated had no effect on fertilizer N requirement on six farms but improved fertilizer N response on the remaining three. In terms of grain and silage response, side dressing 45 kg N/ha was about 120% more efficient than applying it near planting. Results were transferred to more than 400 farmers, farm advisors, State and Federal agricultural agency personnel, and other scientists.
1. High-yielding corn satisfied by alfalfa. The value of legumes, such as alfalfa, to support growth of the next crop has been recognized for at least 2000 years. But can alfalfa still feed today's corn hybrids that produce extraordinary yields? In an extensive set of on-farm trials, ARS scientists at St. Paul, Minnesota, and their university colleagues have shown that alfalfa almost always provides the total requirement of nitrogen for the first corn crop, even when corn yields exceed 230 bushels per acre. This represents a fertilizer savings of more than $80 per acre compared to corn grown after corn. Farmers who avoid excessive fertilizer application will save money and reduce the risk of water contamination by nitrate and also will reduce greenhouse gas emissions.
2. Glyphosate controls rust disease in glyphosate-tolerant alfalfa. Alfalfa producers need new options for controlling foliar diseases that can reduce yields by 10-50% and also reduce forage quality. ARS researchers at St. Paul, Minnesota, found that glyphosate, the active ingredient in Roundup herbicide, completely controlled alfalfa rust on glyphosate-tolerant plants inoculated with the fungus 3 days after glyphosate treatment. The level of protection declined with time after application, indicating that control is transitory and that protective treatments inhibit fungal growth. Complete control of rust was obtained when glyphosate was applied up to 10 days after inoculation with rust spores, indicating that the herbicide also has curative activity. Treatment increased protection from anthracnose disease and reduced symptom severity from spring black stem and leaf spot disease. These results indicate that glyphosate can be used to both reduce weeds and manage foliar diseases in glyphosate-tolerant alfalfa to increase yields and forage quality.
3. Selection of alfalfa for nitrate uptake is successful. Nitrogen is an essential element for crop production, but nitrate, the most important form of nitrogen available to plants, tends to 'get away', polluting water supplies and increasing global warming. ARS scientists at St. Paul, Minnesota, developed new alfalfa lines that were either 1) much better at removing nitrate from the soil to help prevent nitrate losses directly, or 2) less capable of nitrate uptake so neighboring plants, such as grasses, can thrive while removing the nitrate. This new plant selection procedure provides plant breeders a reliable way to change nitrate uptake capacity in alfalfa and other plants, which should lead to better crop production and less environmental damage.
4. Selection of alfalfa for root system architecture is successful. Plant root system architecture is critical for productivity and survival because roots anchor the plant, absorb nutrients and water from the soil, and support helpful bacteria and fungi. Highly branched root systems may be more beneficial under low nutrient supply, whereas highly tap-rooted types may be better at finding water deep in the subsoil during drought. However, the growth environment strongly influences plant rooting. In this research, ARS scientists in St. Paul, Minnesota, found that root system architecture was expressed consistently across environments in alfalfa populations selected for tap- or branch-rooted architectures. Root system architecture also appeared to affect nutrient uptake. If further research confirms these findings, this selection method could be used by public and private plant breeders to produce alfalfas with improved capacity to withstand nutrient, water, and, possibly, mechanical stress, such as frost heaving.Jung, H.G., Mertens, D.R., Phillips, R.L. 2011. Effect of reduced ferulate-mediated lignin/arabinoxylan cross-linking in corn silage on feed intake, digestibility, and milk production. Journal of Dairy Science. 94(10):5124-5137.