Location: Crop Germplasm Research
2020 Annual Report
Objectives
Objective 1: Efficiently and effectively acquire Carya genetic resources; maintain their safety, genetic integrity, health and viability; and distribute them and associated information worldwide.
Sub-objective 1A: Acquire high priority Carya genetic resources, characterize them using molecular profiling methods, integrate them into secure, temporary maintenance systems, and distribute associated information and appropriate propagules worldwide.
Sub-objective 1B: Revise diagnostic methods for detecting Xylella fastidiosa in Carya.
Sub-objective 1C: Screen ex situ and in situ Carya populations for Xylella fastidiosa.
Sub-objective 1D: Confirm efficacy of remediation methods to eliminate Xylella fastidiosa from nuts and/or scions of Carya.
Objective 2: Develop more effective genetic resource conservation, evaluation, and characterization methods and apply them to priority Carya genetic resources. Record and disseminate evaluation and characterization data via GRIN-Global and other data sources.
Objective 3: With other NPGS genebanks and Crop Germplasm Committees, develop, update, document, and implement best management practices for Carya genetic resource and information management.
Approach
This project represents one of the eight National Clonal Germplasm Repositories in the National Plant Germplasm System. It shares the common mission of all clonal repositories to collect, maintain, evaluate, document, and distribute valuable plant genetic resources. It is unique in its focus on the Carya genus, which includes the most valuable nut tree native to North America, the pecan [Carya illinoinensis (Wangenh.) K. Koch]. This project is a sister project of the Pecan Breeding Program (3091-21000-039-00D) and furnishes diverse Carya germplasm for use as parents within that program, as well as to other domestic and international breeding programs. Other North American species of Carya do not provide economic incentive for commercial nut production, but are valuable components of their ecosystems and are represented for use in breeding, with increasing interest on endemic and microbiotic associations. All diploid Carya, including commercially valuable Asian species, hybridize with pecan. Some Carya species exist only as fragmented populations in threatened habitats. Strategies for the appropriate characterization and utilization of those species are addressed in this project. Molecular genetic tools have been developed by the precursor project. These tools will continue to be cooperatively developed, refined, and applied by the current project in order to understand genetic diversity and gene flow in native populations, to verify identity of individual cultivars, to confirm parentage in controlled crosses, and to facilitate management of the Collection and its knowledgeable deployment.
Progress Report
Significant progress was made in fiscal year 2020 on the analysis of critical pecan germplasm to both define the history of the plant, and to identify traits that will provide a better understanding of the genetic makeup of the crop. Under Objective 1, graftwood of two early cultivars ('Kennedy' and 'Randall') that are significantly linked to the domestication history of the pecan, were located, obtained, and grafted at both worksites of the National Collection of Genetic Resources for Pecans and Hickories (NCGR-Carya). Tender leaf tissue of those cultivars were sampled, DNA was extracted, and was resequenced (genotyped). Because of a critical personnel vacancy, a collection trip to Mexico was not done as had been planned. Also under Objective 1, symptom expression related to Xylella fastidiosa was investigated on repository accessions, with some samples being submitted to state diagnostic labs for analysis, and others being sampled, extracted, and stored using improved methods. A limited number of the accessions were screened for Xyllela presence. It was confirmed that Xyllela can be transmitted by seed. Ongoing project work is critical to the solution of this important pecan disease. Under Objective 2, images were acquired using unmanned-autonomous vehicle (UAV) which provided good resolution of tree shape. Under Objective 3, an in-house developed database, and an effective curator's tool for Germplasm Resource Information Network (GRIN)-Global was obtained and installed on project computers. Hundreds of inventory specific images were uploaded to the appropriate database, and indexed. A cooperative project was initiated in which remote images were obtained from project worksites and georeferenced. Work on this project, overall, will facilitate improvement of pecans as an important crop for U.S. producers and consumers.
Accomplishments
1. Improved detection of Xylella in pecan. Xylella fastidiosa causes pecan bacterial leaf scorch disease and has become in recent years a significant obstacle in pecan production. The disease has greatly limited normal activities associated with germplasm distribution by the USDA pecan repository. A better understanding is needed of the syndrome and methods for its detection. ARS researchers at College Station, Texas, working with university and ARS colleagues in Georgia, developed a comprehensive, improved protocol for Xyella detection and monitoring. The work established that Xyella can be transmitted through the seed. This accomplishment is important because the improved protocol provides an efficient tool to detect Xyella disease in orchards. The ability to monitor Xyella accurately is critical to the repository program in the distribution of disease free germplasm both nationally and internationally.
