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Advancing Alfalfa Breeding and Production Research

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ARS advances multiple crop industries by developing new crop varieties with disease resistance and other trait enhancements and providing new tools and approaches that will support future breeding efforts. In addition to supporting major commodities, ARS breeding programs advance specialty crops, which alone have a U.S. farm gate value of $87.7 billion. The following accomplishments are examples of ARS advances in crop breeding for disease resistance and trait enhancement in FY 2019. Hyperlinked accomplishment titles point to active parent research projects.

Alternative fungicide for protecting alfalfa seeds
. Seed rot/damping off of alfalfa is a soilborne disease caused by multiple pathogens that results in thin initial stands of alfalfa plants, lowers forage yields, and reduces survival of plants over the winter. Almost all alfalfa seed is treated with mefenoxam, but this fungicide is not active against the pathogen causing Aphanomyces root rot, a lethal widespread disease of alfalfa, nor against fungal seed rot pathogens. ARS researchers in St. Paul, Minnesota, tested eight alternative fungicides for activity against alfalfa pathogens. At low concentrations, a commercial fungicide containing a mixture of metalaxyl, prothioconazole, and penflufen reduced growth of all alfalfa seed rot and damping off pathogens, including the pathogens not controlled by mefanoxam. Seeds treated with mefanoxam or the fungicide mixture that were planted in soil infested with damping off pathogens were protected from disease. This research provides alfalfa growers with a new tool to reduce damage from Aphanomyces root rot and damping off pathogens of alfalfa.

Planting alfalfa in corn grown for silage protects soil and water resources. Using new management techniques, alfalfa can be planted and grown among corn plants to more quickly bring it into profitable, full forage production the following growing season. Using a rainfall simulator, ARS researchers in Madison, Wisconsin, found alfalfa planted in corn reduced the loss of soil and nutrients from cropland by 40 to 80 percent compared with a conventional system in which alfalfa was planted in the spring, 7 months after corn harvest. Soil sampled at different depths also revealed that alfalfa planted among corn was much more effective than alfalfa planted after corn for rapidly reducing the risk of nitrate leaching to groundwater. Overall, planting alfalfa in corn holds promise for improving farm profitability and for protecting cropland and water resources.

Alfalfa cyst nematode found in North America identified and characterized. Plant-parasitic nematodes cause nearly $10 billion in crop losses annually in the United States. ARS scientists from Beltsville, Maryland, along with researchers from Idaho, Kansas, and Nebraska, determined that features of juvenile and adult nematodes collected from Kansas and Montana alfalfa fields were consistent with the alfalfa cyst nematode. Collectively, the evidence suggests that this represents the first record of alfalfa cyst nematode in North America and may represent an emerging threat to productivity of the alfalfa industry. This information will be used by plant pest management specialists and regulatory officials to manage and potentially contain this nematode to prevent inadvertent movement to additional areas.

Condensed tannins play an important role in alfalfa resistance to root lesion nematode. Condensed tannins are flavonoid oligomers that contribute to many agronomically important plant traits, including disease resistance. Tannins may provide a way to beneficially manipulate protein digestion and prevent pasture bloat in ruminants. Leaves of alfalfa, a major forage crop, contain no detectable tannins that could protect ruminant animals from potentially lethal pasture bloat. Researchers in Beltsville, Maryland, have been working for years to produce tannins in the leaves and stems of alfalfa to prevent pasture bloat in dairy and beef cattle and to suppress internal parasites. They demonstrated that levels of condensed tannins significantly increased in alfalfa roots upon infection with the root lesion nematode. The same mechanisms that contribute to the tannin gain in alfalfa roots during nematode infection can be used to increase tannin concentrations in alfalfa leaves and develop tannin-rich alfalfa cultivars.

New DNA markers for drought resistance and salt tolerance in alfalfa. Drought resistance and salt resistance are important breeding targets for enhancing alfalfa productivity in arid and semiarid regions. An ARS scientist in Prosser, Washington, phenotyped and genotyped a diversity panel of alfalfa accessions consisting of 198 cultivars and landraces. Marker-trait association identified 19 and 15 loci associated with an alfalfa drought resistance index and relative leaf water content, respectively. DNA markers associated with salt tolerance were also identified in a breeding population. Eight drought tolerant/salt resistant alfalfa lines resulting from this project have been transferred to Alforex Seed Company under an ARS material transfer agreement as breeding materials for developing alfalfa cultivars with improved drought resistance/salt tolerance and water use efficiency.

Breeding Insight Platform advances alfalfa breeding efforts. Together with university and private partners, ARS has established the Breeding Insight Platform to accelerate smaller breeding programs through the combination of modern breeding approaches, genomics, and informatics. Thus far, Breeding Insight has leveraged the newly available alfalfa genome sequence to accelerate the development of a genotyping platform for marker-assisted alfalfa breeding.