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United States Department of Agriculture

Agricultural Research Service

Research Project: Enhanced Alfalfa Germplasm and Genomic Resources for Yield, Quality, and Environmental Protection

Location: Plant Science Research

Project Number: 5062-12210-002-00
Project Type: Appropriated

Start Date: Mar 01, 2013
End Date: Feb 28, 2018

Objective:
Objective 1: Develop strategies and tools for improving alfalfa yields, disease resistance, and nutrient cycling efficiency. Sub-objective 1.1: Identify and compare breeding strategies for alfalfa yield improvement. Sub-objective 1.2: Identify strategies and develop tools for reducing losses from diseases. Sub-objective 1.3: Develop strategies to produce alfalfa germplasm with improved herbage yield and nutrient cycling (phosphorus (P) and potassium (K)) in pure stands and in mixtures with forage grasses. Sub-objective 1.4: Develop a gene expression atlas for two divergent alfalfa gene pools (Medicago sativa subsp. sativa and M. sativa subsp. falcata), identify organ-specific genes, and mine sequences for gene pool diversity (SNPs and SSRs). Objective 2: Develop forage germplasm with modified cell-wall structure and chemistry to improve digestibility, and evaluate impacts on livestock and bioenergy productivity. Sub-objective 2.1: Assess alfalfa germplasm altered for in vitro neutral detergent fiber digestibility (IVNDFD) for forage yield and energy availability for livestock production and biofuel conversion efficiency. Sub-objective 2.2: Identify genetic, metabolic, and developmental processes in alfalfa stems that regulate cell wall composition and energy availability. Objective 3: Develop alfalfa germplasm and crop rotation management systems to improve nitrogen cycling and carbon sequestration. Sub-objective 3.1: Identify and utilize mechanisms to improve nutrient uptake in alfalfa. Sub-objective 3.2: Identify and characterize rhizosphere soil microbes that promote carbon sequestration and improve the agronomic and environmental benefits from crop rotation. Sub-objective 3.3: Measure and predict N credits for second-year corn grown after alfalfa to improve N management and reduce N losses.

Approach:
To increase yield potential, the contribution of heterosis to yield potential and the effectiveness of selecting for high yield per stem as a yield component in alfalfa will be assessed. Synthetic populations, semi-hybrid populations, parent populations, and two commercial varieties will be established in replicated field trials and total annual forage yield will be evaluated for at least two production years. We will develop DNA markers to increase disease resistance and measure diversity in pathogen populations. A bulked segregant analysis will be done using populations segregating for resistance to Aphanomyces root rot. Histochemical and gene expression studies will be used to gain an understanding of the infection process and mechanisms of resistance in resistant and susceptible plants. Simple sequence repeat (SSR) markers will be identified in the Verticillium albo-atrum genome sequence and tested for polymorphisms on field isolates and standard strains. Plant responses to these strains will be measured with the standard disease severity scale and the amount of pathogen present determined by the qPCR method. Plants with the lowest amount of pathogen present will be retained, intermated, and progeny tested for Verticillium wilt resistance. DNA markers will also be developed from a gene expression atlas for two divergent alfalfa gene pools using transcripts from leaves, roots, nodules, flowers, and elongating and post-elongation stem internodes. To develop alfalfa germplasm with improved herbage yield and nutrient cycling, germplasm differing in root system architecture will be examined in replicated field experiments to determine: P and/or K uptake capacity under low and adequate soil nutrient levels; symbiosis with arbuscular mycorrhizal (AM) fungi; and prevalence of root and foliar diseases. Alfalfa germplasm selected for in vitro neutral detergent fiber digestibility (IVNDFD) and original parents will be evaluated in replicated field trials for forage quality traits, gain from selection, and heritability estimates. Replicated sward plot field trials will be used to determine forage yield and the best crop management methods for germplasm selected for IVNDFD. Energy availability for livestock and biofuel conversion in the harvested forage will be determined by near infrared reflectance spectroscopy. To improve alfalfa stem cellulose content, a comparison of miRNA profiles in elongating stem and post-elongation stem internodes will be used to identify miRNAs that play key roles in the development of secondary xylem. The microbial communities in the rhizosphere that influence plant growth and carbon sequestration will be characterized using culture-dependent and metagenomics approaches. Field tests will determine whether selection for nitrate uptake alters yields of alfalfa-grass mixtures. On-farm field experiments will be established at 10 locations to improve predictions of whether nitrogen contributed by alfalfa to subsequent corn crops will improve farm profit and reduce nitrogen losses.

Last Modified: 10/21/2014
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