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United States Department of Agriculture

Agricultural Research Service

Research Project: PECAN GENETICS AND IMPROVEMENT
2011 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
The project's pecan scion breeding program during FY 2011 evaluated more than 8,000 controlled-cross seedlings in the Basic Breeding Program (BBP). About two-thirds of the new seedlings were eliminated based upon scab susceptibility. Resistant clones were then budded to pollarded trees or grown on their own roots in BBP evaluation nurseries. The NPACTS (National Pecan Advanced Clone Testing System) test was continued in FY 2011 at College Station, with additional grafting and tree training being accomplished. Data from 21 other NPACTS tests from other sites were added to master data bases to justify future pecan cultivar releases. The performance of two new pecan cultivars released in 2009 (Mandan and Apalachee) was monitored at several national evaluation sites for scab resistance and other characteristics. A new cultivar, Lipan, was released to growers, and graftwood will be disseminated to pecan nurseries this winter. In other FY 2011 research, honeydew produced by aphids on pecan leaves was quantified using water sensitive paper and revealed consistent clonal responses, as well as parental effects. This technique will allow more efficient and accurate rating of aphid resistance in the NPACTS selection program, and ensure more aphid-resistant future USDA cultivar releases. Studies on the genetic control of high oleic fatty acid in pecan kernels was continued, with the investigation of the basic wild population and continued propagation of controlled-cross clones involving the Carden clone, the original high-oleic source. The control of this trait will greatly enhance the nutritional value of the crop by lowering low density serum cholesterol. The goal of developing additional DNA markers related to scab resistance (and other genetic traits) was pursued in FY 2011 through a newly developed cooperative effort with molecular researchers working on Juglans, a sister genus. Existing markers have been used to evaluate a subset of the pecan cultivar collection as well as a core of the provenance collection. The controlled cross mapping population for scab resistance was evaluated in FY 2011 for scab reaction and is currently being sampled for genetic analysis to verify cross integrity. Families from crosses of resistant and susceptible parentage should represent maximum genetic segregation and elucidate genetic control of this important genetic trait. A diverse group of seedstocks planted (in FY 2009) into plots infected with cotton root rot is yielding valuable data; mortality due to the disease has been verified and studies on differential responses are ongoing. Diverse pecan and hickory seedstocks were established in plots infested with the root knot nematode in an effort to identify sources of resistance to this pest. All seedstocks were infested, with no sources of resistance evident.


4.Accomplishments
1. New pecan cultivar for U.S. growers. Pecan is an important U.S. nut crop that is primarily grown by small producers, with most commercial pecan orchards being 20 acres or less in size. Profit margins are minimal for most producers, and there is an ongoing need for new pecan cultivars that will meet specific market niches to enhance marketability and profitability. ARS scientists at College Station, TX, released an improved pecan cultivar to commercial growers and home owners. Lipan is a scab-resistant, high quality pecan, with midseason nut-maturity (early enough to provide a marketing advantage); and is adapted to all pecan growing areas of the world. Nuts are well suited for both the inshell and shelling components of the market, and produce a very high proportion of near perfect halves when shelled, making it highly desirable in preparation of baked and other goods where eye appeal is critical.


Review Publications
Thompson, T.E., Grauke, L.J. 2010. 'Mandan' Pecan. HortScience. 45(9):1392-1393.

Thompson, T.E., Grauke, L.J. 2010. 'Apalachee' Pecan. HortScience. 45(9):1386-1387.

Last Modified: 12/22/2014
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