An extensive working collection of Arachis germplasm is maintained by the USDA at the Southern Regional Plant Introduction Sta. in Griffin, GA. Much of this collection is maintained also under long-term seed storage at the Nat. Seed Storage Lab. in Ft. Collins, CO. The working collection consists of 9027 accessions of A. hypogaea and 684 accessions of Arachis species. About half of the A. hypogaea accessions are unimproved landraces collected in the crop's centers of diversity in South America. The other half is comprised of germplasm obtained from countries outside of South America. The U.S. germplasm collection of peanut was the first major germplasm collection to have a working core collection. Research has verified that this core collection can be used to improve the efficiency of germplasm utilization. This has stimulated a great amount of germplasm evaluation work and has resulted in the identification of numerous sources of resistance to several economically significant pathogens. Considerable efforts in the U.S. also have been devoted to the use of wild species of Arachis for sources of resistance to pathogens. Programs are ongoing to introgress high levels of resistance or immunity to early (Cercospora arachidicola Hori) and late (Cercosporidium personatum Berk. & M.A. Curtis) leaf spots, nematodes, and viruses. Genetic resources have been particularly useful in adding disease resistance to peanut cultivars. This has had a significant economic impact on U.S. peanut farmers. The largest impacts have been from the development of cultivars with resistance to Sclerotinia blight (Sclerotinia minor Jagger), the peanut root-knot nematode [Meloidogyne arenaria (Neal) Chitwood race 1], and tomato spotted wilt Tospovirus. Use of these resistant cultivars has an estimated economic impact of more that $200 million annually for U.S. peanut producers.