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United States Department of Agriculture

Agricultural Research Service


Location: Crop Germplasm Research

2009 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)
Research objectives will be met by basic genetic research and by an intensive cultivar and rootstock selection program. These improvements will be accomplished through several approaches. Phenotypic breeding techniques, supplemented with molecular tools, will be used to develop and release new pecan scion cultivars with high yield and quality, and exhibiting improved disease and insect resistance. Similar approaches will be utilized to develop superior pecan rootstocks with outstanding vigor and salt tolerance. Qualitative and quantitative techniques, in conjunction with molecular techniques, will be used to elucidate the genetic control of key horticultural traits in pecans. Genetic research conducted by this project will increase our knowledge of the genetic control of yield components, nut maturity, nut quality, tree size, and disease and insect resistance. The scion cultivar development component of the work will produce precocious, high-yielding, regular bearing, disease- and insect-resistant cultivars that also have high nut quality. Rootstock breeding activities will produce new rootstocks with improved vigor, uniformity, salt tolerance, disease and insect resistance, and specific geographical adaptation; and which will ultimately contribute to increased yields of grafted scions.

3. Progress Report
Work under this project during FY 2009 included screening for pecan scab resistance in the Basic Breeding Program (BBP). More than 320 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 ensure future adequate nut production. More than 120 clones from interspecific hybridization efforts between pecan and a species of hickory (Carya cordiformis) were grafted to large pecan trees to decrease time to flowering so that future selections and crossings will be expedited. Yield and other evaluation data from NPACTS (National Pecan Advanced Clone Testing System) were summarized and added to project-maintained databases that are accessible to other pecan researchers worldwide. In the project's molecular genetics work, sophisticated molecular biology techniques were used to identify in pecan three genetic markers from chloroplasts (the bodies within plant cells that make chlorophyll). These markers will be useful in establishing the maternal inheritance traits in various pecan types.

4. Accomplishments
1. Using Molecular Biology to Develop Better Pecans: Pecan is an important nut crop in the U.S., and there is need to better understand the genetic make-up of the species so that improved pecan varieties can be developed. We used modern and sophisticated molecular biology techniques to examine in great detail the genetic make-up of more than 150 different pecan types. The work developed and utilized tools known as plastid primers to make these genetic analyses, which showed great variety in the genetic characteristics of different pecan types, and identified both those that were very similar if not almost identical, and those that were quite different. Pecan types from Asia and from Mexico were very different genetically from U.S. types, indicating a very long history of isolation and genetic divergence. This accomplishment is important because it provides foundational genetic information that will effectively guide ongoing genetic and breeding efforts aimed at developing more productive, pest/disease resistant, and nutritious pecans that will benefit both producers and the consumer.

2. New Pecan Cultivars for U.S. Growers: Pecan is an important U.S. nut crop that is primarily grown by small producers; most commercial pecan orchards are 20 acres or less in size. Profit margins are minimal for most producers, and there is ongoing need for new pecan varieties that will meet specific market niches to enhance marketability and profitability. We have released two new, improved pecan cultivars to commercial growers and home owners. Mandan is an early nut-maturing cultivar suited to all pecan growing areas of the world; Mandan nuts mature earlier than any other variety which will provide marketing advantages to those who utilize it significantly in their orchards. Mandan is also resistant to pecan scab disease, and its nut is well suited for both the inshell and shelling components of the market. Apalachee is a small, high-quality pecan that produces a very high proportion of perfect, quality halves when shelled and which will make it highly desirable in preparation of baked and other goods where eye appeal is critical. Apalachee is adapted primarily for use by growers in the southeastern U.S.

Review Publications
Venkatachalam, M., Kshirsagar, H.H., Seeram, N.P., Heber, D., Thompson, T.E., Roux, K.H., Sathe, S.K. 2007. Biochemical composition and immunological comparison of select pecan [Carya illinoinensis (Wangenh.) K. Koch] cultivars. Journal of Agricultural and Food Chemistry. 55:9899-9907.

Last Modified: 07/27/2017
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