Location: Crop Germplasm ResearchTitle: The forest and the trees: Applications for molecular markers in the Pecan Breeding Program
Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/22/2014
Publication Date: 2/15/2015
Citation: Grauke, L.J., Klein, R.R., Grusak, M.A., Klein, P. 2015. The forest and the trees: Applications for molecular markers in the Pecan Breeding Program. Acta Horticulturae. 1070:109-126.
Interpretive Summary: The USDA ARS Pecan Breeding and Genetics program maintains worldwide sources of genetic diversity for the genus Carya, and uses those materials in breeding to improve pecan, a large, long-lived perennial tree with long generation time. Development of molecular genetic markers by this program has contributed to understanding diversity of the genus, as well as refining the identification and selection of the improved cultivars being used in the pecan industry. Crop wild relatives have influenced important pecan cultivars being used in breeding, as revealed by molecular markers in these studies. The identity of historic and recent pecan cultivars has been illuminated by the use of our markers, refining our understanding of parentage and providing reliable profiles for the maintenance of verified accessions. Development of improved methods of marker assisted selection will require continued cooperative effort, working on the secure base of diversity provided by this program, and working with the tools that are being developed in this research.
Technical Abstract: Inventory specific verification of accession identity is crucial to the function of the National Collection of Genetic Resources (NCGR) for Pecans and Hickories, and is an increasingly important component of the USDA ARS Pecan Breeding Program. The foundation of the NCGR is the living trees maintained in our orchards. Those trees are linked to historical records, physical vouchers, molecular profiles, and performance evaluations that provide a dynamic reference for domestic and international germplasm users, including future breeders. The mandate of the NCGR is to collect from "worldwide sources of wild species and domestic cultivars to provide for maximum genetic diversity in each genus". As molecular marker technology advances, it provides a window to the forest as well as to the trees, if appropriate samples are selected from the ex situ collection. Interspecific hybridization has been documented between sympatric populations of Carya species using simple molecular markers, providing evidence to identify introgression of genes that may have value in breeding while raising questions of regional patterns of adaptive diversity. Within the cultivar collection, those markers provide verification of identity and parentage that at times requires a reanalysis of historical records and impacts the potential use of accessions. The careful interpretation of molecular data may impact strategies for both the composition of germplasm collections and the direction of breeding programs. Case studies are presented highlighting recent work related to 'Major', 'Schley', 'Byrd' and USDA 1963-16-0182. Strategies of test design as well as marker development are addressed. Implications for domestic and international cooperation in both germplasm exchange and database utilization are noted.