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ARS Home » Plains Area » College Station, Texas » Southern Plains Agricultural Research Center » Crop Germplasm Research » Research » Research Project #412805


Location: Crop Germplasm Research

2008 Annual Report

1a. Objectives (from AD-416)
The long-term goal of this project is to produce improved scion and rootstock cultivars for the U.S. pecan industry. The project will also elucidate genetic control of important pecan traits using traditional and molecular genetics techniques. Over the next 5 years we will focus on the following objectives: Objective 1: Enlist phenotypic breeding techniques, supplemented with molecular tools, to develop and release new pecan scion cultivars with high yield and quality, and improved disease and insect resistance. Sub-objective 1.A: Develop high yielding pecan scion cultivars with early nut maturity, improved nut quality, and superior disease and insect resistance. Sub-objective 1.B: Develop DNA markers to identify genetic variability and enhance the selection of superior scion cultivars. Objective 2: Enlist traditional selection techniques and newly developed molecular tools, to develop superior pecan rootstocks with outstanding vigor and salt tolerance. Sub-objective 2.A: Establish patterns of variation in pecan seedlings as a function of geographic origin. Sub-objective 2.B: Develop additional molecular genetic tools for use in pecan, including markers based on sequences of the chloroplast genome and capable of discriminating between accessions of pecan on the basis of maternal inheritance. Objective 3: Apply qualitative and quantitative techniques, in conjunction with molecular techniques, to elucidate the genetic control of key horticultural traits (such as yield level, nut size, time of nut maturity, salt tolerance, and disease and insect resistance) for pecans. Sub-objective 3.A: Elucidate the genetic control of key horticultural traits in pecan utilizing appropriate qualitative and quantitative techniques. Sub-objective 3.B: Establish families of controlled cross seedling pecans suitable for use in mapping qualitative and quantitative trait loci related to scab disease resistance, and to determine levels of scab resistance within those progenies.

1b. Approach (from AD-416)
1. Segregating family progenies in replicated yield tests will be characterized for many genetic characteristics such as yield level, time of nut maturity, nut size, and disease and insect resistance. Type of inheritance of each characteristic will be determined, as well as genetic association between traits. Various modifications of budding techniques to shorten generation time will be tested. 2. Parents are selected, crosses are made, seedlings are grown and evaluated in the BBP (Basic Breeding Program), and the best clones are selected and further tested in NPACTS to identify superior clones that are released to growers as improved cultivars. 3. Parents are selected, crosses are made, seedlings are grown and evaluated in the field, and the best clones are selected and further tested in NPACTS to identify superior clones that are released to growers as improved rootstock cultivars.

3. Progress Report
This is a new project tjat replaced 6202-21000-021-00D and which is continuing and expanding upon the work of the precursor project. Work under this project during FY 2008 included screening for pecan scab resistance in the Basic Breeding Program (BBP). More than 1,000 controlled-cross seedlings from prior years were rated for scab resistance. More than 15,000 controlled-cross seedling trees in the BBP were selectively thinned to insure future adequate nut production. More than 120 clones from interspecific hybridization efforts between pecan and Carya cordiformis were grafted to pollarded trees to decrease time to flowering so that clonal selection and crossing would be expedited. Yield and other evaluation data from NPACTS (National Pecan Advanced Clone Testing System) were summarized and added to project-maintained databases. In the project's molecular genetics work, two chloroplast markers were identified from among five universal chloroplast primers tested that can distinguish clones on the basis of maternal inheritance, allowing determination of common maternal parentage. Separation of the chloroplast polymorphism was possible using standard PCR procedures and capillary electrophoresis. (NP 301, Component 3, Problem Statements 3.A, 3.B, 3.C)

4. Accomplishments
1. Chloroplast Markers for Pecan: Pecan rootstocks influence performance of trees in orchards, but few tools are available to study differences that might arise from different open-pollinated seedstocks. Scientists in the Crop Germplasm Research Unit at the Southern Plains Agricultural Research Center, College Station, Texas, in cooperation with scientists at Texas A&M University, tested five prospective universal chloroplast primers. Two of the primers were qualified as informative for pecan; amplifying base pair differences capable of being consistently separated using capillary electrophoresis after routine Polymerase Chain Reaction studies were done. This accomplishment is important because it provides simple methods to study the mixing of genomes in interspecific hybridizations as well as the distribution of diversity in relation to geography, contributing to an understanding of rootstock adaptations and recommendations for deployment. Ultimately, application of these and other markers to pecan development will result in improved cultivars for use by producers. (NP 301, Component 3, Problem Statement 3.A).

5. Significant Activities that Support Special Target Populations