Germplasm collection, genetic resources, and gene pools in alfalfa

Authors: Irish, Brian; Greene, Stephanie

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 6/7/2021
Publication Date: 7/18/2021
Citation: Irish, B.M., Greene, S.L. 2021. Germplasm collection, genetic resources, and gene pools in alfalfa. In: Yu LX., Kole C., editors. The Alfalfa Genome. Compendium of Plant Genomes. Springer. Cham, Switzerland. p.43-64. https://doi.org/10.1007/978-3-030-74466-3_4.
DOI: https://doi.org/10.1007/978-3-030-74466-3_4

Interpretive Summary: Alfalfa is one of the most important forage legume species in the world. Collections of genetically diverse alfalfa, and many of its wild relatives, are conserved in genebanks so they are available to be used by plant breeders and scientists to improve alfalfa production. One of the more prominent collections, with over 13,000 individual unique samples, is held by the USDA, ARS National Plant Germplasm System. These plant collections are actively managed involving, among other things, acquisition to fill collection gaps, seed increase, characterization, evaluation, and distribution. Detailed record keeping, accomplished by use of customized computer software, is critical as collections have substantial associated historical, taxonomic and characterization and evaluation data. The United States alfalfa collection and its data are held in the public domain and seed is freely available in small quantities for research and educational purposes. Over the years access to these collections have benefited plant breeders and producers by providing access to traits (e.g., disease resistance) for improved cultivar development expanding growing areas and sustainable production of the crop.

Technical Abstract: Popular for its feed quality and benefits to the environment, alfalfa (Medica sativa L.) is the most economically important forage legume crop in the world. Most agricultural crops have plant genetic resource (PGR) collections that are conserved, with their use promoted by national and international genebanks. Large alfalfa germplasm collections are held, in the form of seed, in genebanks worldwide. These same genebanks also are responsible for many other cultivated species and alfalfa crop wild relatives (CWR) in the genus Medicago. Once acquired, these taxonomically diverse collections are actively managed, requiring ideal storage to promote longevity, regeneration activities to resupply viable seed, and sample duplicates to safeguard against loss. Extensible database software platforms continue to expand capabilities for maintaining fidelity and public access to accession-associated information. As resources and policies allow, PGR are distributed to stakeholders (e.g., plant breeders) in public, non-profit and private research sectors. Many of the PGR have been extensively characterized and evaluated for important phenotypic, agronomic, and genetic traits. As many of the alfalfa and other Medicago spp. collections are too large to evaluate at once, subsets of representative genetically distinct accessions (i.e., core collections) have been established and evaluated. Data generated in characterizations and evaluations are often linked to accessions and continue to expand, helping users identify useful germplasm. Although difficult to assess because alfalfa and many Medicago spp. accessions are often heterozygous outcrossing polypoid populations, comprehensive genetic diversity has been described for some of the larger collections. Diversity and accession numbers for CWR collection holdings is much lower, although the potential value in introgressing key traits from germplasm in these genepools has been shown. In the United States, early plant germplasm introductions played important roles in breeding modern alfalfa cultivars. Many of these traits (e.g., cold adaptation and biotic/abiotic resistance) have contributed to expanded growing areas and sustainable production. Historically, production of alfalfa and other Medicago spp. forages has benefited from the diversity conserved in PGR collections. Continued access to these critical Medicago spp. PGR will only be secure if committed support from stakeholder communities endures.