Location: Crop Germplasm Research
Project Number: 3091-21000-046-000-D
Project Type: In-House Appropriated
Start Date: Jan 18, 2023
End Date: Jan 17, 2028
Objective 1: Conduct research to develop genetic resource maintenance, evaluation, or characterization methods and, in alignment with the overall NPGS Plan, apply them to priority Carya genetic resources to avoid backlogs in genetic resource and information management. Sub-objective 1.A: Improve the accuracy of phenotyping for pecan traits, specifically pecan scab susceptibility, through improved rating scales and computer image processing. Sub-objective 1.B: Determine the distribution of Xylella fastidiosa in pecan seeds, roots, and throughout the canopy during the growing season. Determine seed transmission rates and subspecies level differences of X. fastidiosa in various improved pecan cultivars. Objective 2: Acquire; maintain the safety, genetic integrity, health, and viability; and distribute priority Carya genetic resources and associated descriptive information. Sub-objective 2.A: Strategically maintain, expand, and increase the health and longevity of germplasm contained in the orchards of the NCGR-Carya. Sub-objective 2.B: Identify and apply species-diagnostic SNPs to validate species/hybrid identity and to guide repository germplasm acquisition efforts. Sub-objective 2.C: Validate the effectiveness of cryopreserved pollen in controlled crosses and expand the representation of Carya pollen in cryopreservation at the National Laboratory for Genetic Resources Preservation (NLGRP). Objective 3: Characterize priority horticultural traits, genetic pathways, physiological processes, and genotypic markers to support pecan breeding, and elucidate the genomic structure for pecan and related Carya species. Sub-objective 3.A: Identifying QTLs for growth, disease, and nut quality traits for pecan breeding using bi-parental mapping populations. Subobjective 3.B: Validate existing QTL for bud break and scab resistance and develop GWAS trait associations in repository and breeding populations. Sub-objective 3.C: Evaluate the contribution of non-structural carbohydrates on patterns of alternate bearing and shoot carbohydrate storage in pecan. Objective 4: Breed pecan scion cultivars with superior horticultural traits, host-plant resistance, and tolerance to biotic and abiotic stresses, and select regionally adapted pecan rootstocks. Sub-objective 4.A: Develop high-yielding pecan scion cultivars with a compact tree form, early nut maturity, high-quality kernels, and superior disease and/or insect resistance. Sub-objective 4.B: Examine the effects of open-pollinated rootstocks on pecan scion vigor, nut production, and nut quality.
The USDA-ARS Pecan Breeding and Genetics program houses two major initiatives: 1) A nationally focused Pecan Breeding Program responsible for releasing 32 pecan cultivars since 1930 and 2) The National Collection of Genetic Resources for Pecans and Hickories (NCGR-Carya). Our research addresses many problems facing pecan growers, researchers, and consumers. In this research plan, we address six main concerns: Conservation of genetic diversity (Sub-objective 2.A, 2.B), pollen cryopreservation (2.C), infections of Xylella fastidiosa (1.A, 1.B), pecan breeding (4.A), associating important pecan traits with genetics (3.A, 3.B), and physiological issues affecting pecan nut yields (3.C, 4.B). Conservation of genetic diversity is the primary function of the living repository NCGR-Carya managed by the project. Items of deferred maintenance (fencing, tree removal, etc.) and structural improvements (e.g., irrigation) related to a changing climate are needed for the continued efficient operation of these diverse orchards. Pollen cryopreservation benefits the breeding program by providing another avenue of conservation and enabling crosses when pollen may not be available. Xylella fastidiosa is a major plant pathogen, and its presence in the repository and breeding material presents challenges for distribution and breeding. A better understanding of X. fastidiosa biology will facilitate the development of Integrated Pest Management approaches for control. Pecan breeding provides new varieties to the pecan industry, which are likely the best way to address the long-term challenges of a changing climate. Few associations between genetics and important pecan traits exist, and developing more will accelerate the speed and efficiency of pecan breeding. Finally, the entire pecan industry grafts scion clones onto open-pollinated seedlings as rootstocks. The degree of rootstock effects have not been fully quantified in pecan. Successful investigations in these six areas will benefit the long-term viability and usefulness of the NCGR-Carya repository and the development of high-quality varieties for the pecan industry.