Dynamic Use of the National Collection of Genetic Resources for Pecans and Hickories

Abstract

Our unit was initially designated as a USDA Agricultural Research Service National Clonal Germplasm Repository based on an existing collection of grafted cultivars developed for use as parents by the USDA ARS Pecan Breeding Program. From its inception, the NCGR- Caryahas pursued a dynamic collection strategy with three distinct targets: 1) collection of named cultivars from culturally distinctive growing regions to represent selections made over the 170+ year history of grafting pecans; 2) provenance collections of self-rooted seedlings to represent genetic diversity in the context of geographic origin; 3) representative collections of Caryaspecies to provide the broadest base of potentially compatible genetic diversity. The entire collection is maintained as living plant inventories at two worksites in Texas, where 5 ARS workers maintain trees on 242 hectares. Graftwood distributions have historically been requested from only a small subset of accessions, primarily the most recently released cultivars, while seed distributions have been from a small subset of primarily standard seedstock sources. Graftwood exchange is impacted by the presence of disease caused by the bacterial pathogen Xylella fastidiosa. The broad genetic diversity available in the collection is being used by multiple international teams for developing improved methods of molecular characterization based on genome sequencing. Inventory specific records of NCGR- Caryaprovide the “type” collections for genomic profiles of taxonomic species and are a particularly valuable laboratory for studying interspecific hybridization. Phenotypic records linked to pecan provenance inventories in replicated test configurations provide evidence of regional adaptation related to genetic diversity that varies between geographic subpopulations. Historically documented passport records of regional pecan cultivars linked to their phenotypic and genomic characterizations provide the foundation for identity verification procedures and tools for development of marker assisted selection. This accessible, diverse, living collection of trees is contributing to the development of the next generation of Caryascientists, as they work toward the refinement of improved genomic techniques. The next generation of breeders will use these tools to select cultivars with traits targeted for improved regional performance from broad foundations of genetic diversity available within the collection. Long-lived test systems on NCGR- Caryaworksites will provide foundations for future development of improved techniques such as remote imaging. As this generation of breeders works cooperatively within these diverse collections, we hope to facilitate continued coordinated use. Cryopreservation of pollen from selected inventories is being pursued in conjunction with scientists at the USDA National Center for Genetic Resources Preservation, Fort Collins, CO.