CRIS Project No.: 6207-21000-006-00D
Title: Genetics and improvement of pecan (Breeding)
Scientists: Dr. T. E. Thompson, Research Geneticist, GM-14,
.70
Dr. L. J. Grauke, Research Horticulturist, GS-12, .40
OBJECTIVES:
The primary purpose of this project is to increase pecan production through the development of improved cultivars and rootstocks. This goal is being attained by a straightforward genetic selection program, supplemented by basic genetic research. The selection program is targeted at originating new, early maturing, precocious, high yielding, regular bearing, disease and insect resistant, high quality pecan cultivars. This is the only pecan breeding program in the world. Regionally adapted improved rootstocks can contribute to tree performance and, ultimately, to increased yield of grafted scions. In the process of selecting improved cultivars and rootstocks, improved selection methods are developed. Basic genetic research contributes to parental selection as well as earlier and enhanced selection of progeny. Specific objectives are to increase knowledge of genetic aspects of yield in pecan and to increase resolution of genetic contributions to environmental adaptations of both rootstocks and scions.
NEED FOR RESEARCH:
Pecan is the most valuable native North American nut crop. It is the most important nut crop grown in Mexico and is grown to some extent in Israel, S. Africa, and Australia. Pecan has traditionally been grown commercially in the southern U.S. from Texas to Florida. Production is increasing in some of the southwestern states. The proportion of U.S. production (by weight) from improved cultivars has been increasing steadily. Native stands continue to be flooded, bulldozed, and otherwise eliminated.
Only Texas, Oklahoma, and Louisiana have sizable areas of natives while smaller areas are reported for five other states. The U.S. total of about 340,000 ha includes all solid stands of natives and accounts for 59 percent of the total U.S. pecan areas, but only 30 percent of total production.
Generally, native pecan nuts return less per unit weight than those from improved cultivars. A recent three-year average price per kg of natives was $1.73 compared to $2.44 for improved. This same publication reported the average yearly value of the total U.S. crop (native plus improved) to be $259 million for 125 million kg produced.
There is no higher priority long-range research need for this crop than increasing yield through breeding. There are also disease and insect problems that must be addressed by breeding resistant cultivars (see Genetic Resistance project). Pecan orchard managers compete for a market with nut crops such as Persian walnut which require comparable management, but routinely yield twice as much as pecan. Furthermore, the price paid for pecans is depressed by abundant (albeit erratic) production from unmanaged orchards of both native and improved pecan trees. Significant progress must be made by genetic selection within the species for high, regular yields under reduced management if the improved pecan industry is to survive.
The long-term nature of this project and its scope, both geographically and academically, make institutional stability as well as multidisciplinary and interregional cooperation necessary. The physical location of the pecan genetics program and orchards in proximity to faculty and resources of Texas A&M University and key laboratories of the USDA-ARS Southern Plains Area are a significant asset.
The project will benefit the improved pecan industry directly through the development of more productive and, therefore, more profitable cultivars and rootstocks. Consumers of pecans will be indirectly benefited by the enhanced production and market stability which will accompany the enhanced economic position of improved pecan production. By developing pest resistant cultivars, this research will reduce production costs and environmental pollution, benefiting both producers and the general public.
APPROACH AND PROCEDURES
Genetic Selection
Cultivar Breeding. The basic breeding program and the National Pecan Advanced Clone Testing System (NPACTS) produce improved scion cultivars. This is a very labor intensive effort, but it is also the best investment that can be made in the future economic worth of this crop. The continued development of NPACTS allows the rigorous determination of clonal genetic responses across environments. This knowledge adds greatly to our ability to breed pecans for specific environments and enhances our basic understanding of this species.
The following selection scheme is used in the basic breeding program and in NPACTS:
PhaseDescriptionYears# Clones/YrSpacing (ft)IControlled crosses13000-5000(nuts harvested)IIScab Screening2-38000-10,0001 X 10IIIInitial Selection103000-600010 X 15IVNPACTS10-1510-1535 X 35In Phase I, the traditional crossing technique is used to produce up to 5,000 seed each year. This large amount of seed is possible by improved techniques of tree preparation and care so each crossed cluster produces more seed. All seed produced by these hand crosses is planted directly in the greenhouse, and seedlings are measured for growth parameters during the first year. The seedlings are then transplanted to the orchard (Phase III or the Basic Breeding Program (BBP)).
Seed for Phase II is produced in areas isolated from undesirable pollen sources. These are usually orchards that contain only two cultivars that interpollinate and, therefore, produce primarily seed of known male as well as female parentage. Seed is planted, and seedlings are grown at close spacing, under conditions that encourage natural scab infection. Resistant seedlings are selected and enter Phase III testing.
Phase III is the initial selection phase at Brownwood and College Station for yield, tree size increase, precocity, nut quality, disease and insect resistance, desirable leaf and tree structure, etc. Only about 0.5% of these clones are saved for Phase IV (NPACTS) testing.
During Phase IV, elite clones from Phase III are tested in replicated trials across the pecan belt, mainly for environmental adaptation (see "NPACTS Procedures" below). NPACTS consists of 16 locations, from Florida to California and north to Nebraska (Appendix 1, Figure 1). Testing is often done cooperatively with private growers, state experiment stations, state agricultural extension services, and universities. For instance, NPACTS tests are currently established at College Station in cooperation with the Texas Agricultural Experiment Station. Clones which perform well in these NPACTS tests are released as new cultivars. A new cultivar could be released every 2-5 years. About 20,000-50,000 clones are screened in the entire breeding program to produce a single new cultivar. This figure seems quite realistic from a genetic standpoint when projected heritabilities of different traits are considered.
Rootstock Selection. Rootstock selection is based primarily on parameters of performance within the range of climatic (and possibly edaphic) adaptation. Necessary attributes of commercial seedstock include: rapid growth (required for nursery production); uniformity (required for nursery production); precocity (required for orchard production); and productivity (required for orchard production). In order to establish criteria for selection of seedstocks, commercially selected seedstocks are grown and contrasted in the screenhouse and under orchard conditions. The influence of seed quality and parentage on initial seedling vigor is being evaluated.
PROGRESS:
Program development
Data from breeding nurseries and existing NPACTS orchards has been organized into a relational database accessible to a personal computer, speeding access to data. Routine procedures for evaluating growth of first year controlled cross seedlings have been implemented, for determining parental and seed quality effects on seedling vigor.
Cultivar development
Southeastern region
Recent releases include Oconee and Houma, two disease resistant cultivars targeted especially at the humid southeastern production area. Heritability of scab disease resistance in controlled cross families has been reported, influencing parental selection for increased recovery of resistant seedlings.
NPACTS test orchards have been established in Alabama (Baldwin and Elmore Counties), Florida (Gulf County), Georgia ( Peach and Tift Counties), Louisiana (Caddo Parish), Mississippi (Washington County), and Texas (Atascosa, Brown and Burleson Counties).
Western region
Based on data accumulated in cooperation with Dr. J. Benton Storey from NPACTS orchards in Burleson County, TX, the pecan cultivar Navaho was released in 1994, targeted for use in the Western production area. NPACTS test orchards have been established in California (Tulare County).
Northern region
The pecan cultivar Osage was recently released, targeted specifically for use in the Northern pecan region, due to its cold hardiness and increased nut size as compared to alternative cultivars. A seedling nursery containing controlled cross pecan seedlings with Northern pecan parentage has been established in Kansas, in cooperation with Dr. Bill Reid, in an effort to improve selection of regionally adapted cultivars. NPACTS test orchards have been established in Kansas (Labette County), Missouri (Bates County), Nebraska (Lancaster County), and Oklahoma ( Payne and Kay Counties).
Rootstock development
Families of open pollinated seedstocks have been distinguished for their influence on patterns of spring growth and resultant susceptibility to freeze damage. Rootstock usage throughout the pecan industry has been surveyed and patterns of usage reported. The necessity for climatic adaptation in nursery seedstocks is reflected in regional usage patterns, while patterns of edaphic adaptation are less apparent. Altered patterns of nursery procurement as a function of state insect quarantines have affected access to preferred seedstocks in Arizona, sending growers to California nurseries for trees. Researchers, nurserymen and growers have been cautioned concerning possible problems with the use of some California seedstocks in the high desert area of Arizona, due to early fall freezes. Evaluation of data from a rootstock test orchard in Louisiana indicates altered patterns of nutrient uptake as a function of seedstock. Arizona pecan growers having particular rootstocks have been cautioned to evaluate boron status of soils and waters, and to monitor leaf concentrations. Patterns of graft compatibility and leaf chlorosis have been related to seedstock species in a population of pecan, water hickory and Carya Xlecontei hybrid rootstocks. Researchers, nurserymen and pecan growers have been cautioned about the use of water hickory as a rootstock in the Southeast. Test orchards have been established for use in determining patterns of nutrient uptake as a function of seedstock provenance.
PLANS:
National Program coordination:
The breeding program is the most important project and will be maintained as long as the program functions. In the face of reducing budgets and personnel, fewer controlled crosses can be made, maintained, and evaluated. In the NPACTS program, travel to service other NPACTS locations is not possible. This reduces the control and productivity of NPACTS tests. With reduced input from this program, the quality and amount of research data from other locations has declined dramatically in recent years. Increased efficiency in the production of controlled-cross nuts, improved methods of data handling, and improved data collection methods (provided by this program) can not overcome lack of testing at other regional test sites. Since this is a national program, it is imperative that ARS management decisions be made to insure the adequate testing of this material in other areas.
The effort to develop genetically improved pecan cultivars is impeded by cultural systems that obscure cultivar potential. Reduced budgets prevent optimum management, even in orchards under the direct control of this program, due to inadequate equipment, labor, and materials. NPACTS test orchards are the perfect laboratory to develop improved methods of site characterization, irrigation monitoring, and to study differences in cultivar response to uniform culture (from phenology of growth, bloom and nut maturation to differences in nutrient uptake). Such information could provide the basis for modelling improved ideotypes of pecan.
To the extent possible, we will pursue genetic research in the following areas: 1) eliminate alternate bearing in pecan by producing early nut maturing cultivars; 2) develop a two year breeding program; 3) define heritabilities of important nut and tree characteristics; 4) define components of yield and modify selection accordingly; and 5) define environment X genotype interactions using NPACTS data.
Biotechnology strategy:
The use of molecular markers to enhance plant breeding efforts is being widely tested in several crop species. However, no DNA markers are available to use in pecan breeding. The development of molecular markers could substantially increase our understanding of genetic systems in pecan, improve the effectiveness of the pecan breeding program, and contribute to the development of strategies for the conservation of this important native North American tree.
To be effective, strategies must be developed that clearly delineate goals and set priorities consistent with the constraints of the program. To pursue those goals, partnerships must be developed between specialists having knowledge of and access to structured plant populations and specialists having knowledge of and access to molecular techniques. We were involved in cooperative efforts directed by Dr. M. Stine (Louisiana State University, Forestry) who evaluated use of RAPD (random amplified polymorphic DNA) markers within controlled cross families from the Pecan Breeding program, as well as within less structured collections of native trees from a provenance collection.. A limitation of the work was the relatively small number of primers used (56 screened). The researchers concluded that linkage maps could be constructed in full-sib F1 families with 40 or more progeny (60-100 optimum) (Stine, personal communication). The breeding nurseries of this program are the perfect laboratory for the development of those markers.
We have outlined a strategy for the use of biotechnology for the development of marker aided selection within the Pecan Breeding Program. The strategy is based on cooperation between scientists of the Pecan Breeding & Genetics Unit, located in College Station, Texas, and Dr. Sam Reddy, a research scientist in the Texas A&M Biotechnology Center. The long term goal of this research is to provide molecular markers for use in the breeding program, and for genotyping. The immediate
An average of 2000 seedlings are produced each year in the Pecan Breeding Program. Effective early methods for screening disease resistance could allow concentration of limited resources toward maintenance and evaluation of identified superior seedlings. Tagged markers for the selection of other important traits, such as tree and nut maturity dates, components of nut quality (nut size, percent kernel, kernel color, oil composition, etc.) and components of yield (cluster size and distribution, etc.) will be pursued in subsequent work.
Rootstocks.
Open-pollinated seedlings have been grown from seedstocks that represent the range of cold-hardiness in pecan. Those seedlings will be used in research to characterize freeze tolerance of seedstocks, in an effort to improve selection criteria for regional rootstocks. An orchard will be established for continuing research on the influence of seedstock on phenology of stions.
A competitive grant proposal has been prepared seeking funding to evaluate seedlings collected across diverse sites for enhanced ability to uptake zinc. The selection of seedstocks with increased zinc uptake ability could contribute greatly to the western pecan industry.
COOPERATORS:
Mr. E. L. Fitzgerald, Dr. Bill Goff, Dr. W. A. Gustafson, Mr. Monte Nesbitt Dr. R. D. O'Barr Dr. Bill Reid Mr. Wes Rice, Mr. Steve Sibbett, Dr. Michael T. Smith, Dr. Michael W. Smith, Mr. Keith Walden, Dr. Bruce Wood, Dr. Morris Smith, Dr. Ray Worley, Mr. Clay Zowarka,
Publications (Last 3 years):
1 . Grauke, L.J. and Pratt, J.W. 1992. Pecan bud growth and freeze damage are influenced by rootstock. J. Amer. Soc. Hort. Sci. 117:404-406.
2. Grauke, L.J. and Thompson, T.E. 1992. Patterns of pollination in pecan. Proc. Tex. Pecan Grow. Assoc. 66:41-49.
3. Senter, S.D. and Thompson, T.E. 1992. Lipid profiles of pollen from six pecan cultivars. Annu. Rep. North. Nut Grow. Assoc. 83:63-67.
4. Grauke, L.J. and Thompson, T.E. 1993. The effect of season on dichogamy patterns in pecan. HortScience 28(4):266. (Abstract)
5. Grauke, L.J. and Thompson, T.E. 1993. The effect of season on dichogamy patterns in pecan. Proc. Southeast. Pecan Grow. Assoc. 86:66-86.
6. Grauke, L.J. and Thompson, T.E. 1993. Variability in pecan flowering. Proc. Northern Nut Growers Assn. 84:81-94.
7. Grauke, L.J. 1993. Pecan Pollination. Chapter III p. 5-11. In: G.R. McEachern and L.A. Stein (eds.) Texas Pecan Handbook (TAES Horticulture Handbook 105).
8. Grauke, L.J. 1993. Pecan Rootstocks. Chapter III p. 13-15. In: G.R. McEachern and L.A. Stein (eds.) Texas Pecan Handbook (TAES Horticulture Handbook 105).
9. Halloin, J.M., Cooper, T.G., Potchen, E.J. and Thompson, T.E. 1993. Proton magnetic resonance imaging of lipid in pecan embryos. J. Am. Oil Chem. Soc. 70(12):1259-1262.
10. Thompson, T.E. and Baker, J.F. 1993. Heritability and phenotypic correlations of six pecan nut characteristics. J. Am. Soc. Hortic. Sci. 118(3):415-418.
11. Thompson, T.E., Senter, S.D. and Grauke, L.J. 1993. Lipid content and fatty acids of pecan pollen. HortScience 28(12):1191-1193.
12. Thompson, T.E., Senter, S.D. and Grauke, L.J. 1993. Lipid content and quality of pecan pollen. HortScience 28(4):264. (Abstract)
13. Thompson, T.E., Senter, S.D. and Grauke, L.J. 1993. Lipid content and quality of pecan pollen. Proc. Southeast. Pecan Grow Assoc. 86:145-151.
14. Ou, Shyi-Kuan, Storey, J.D. and Thompson, T.E. 1994. A northern pecan pollen source delays germination of nuts from a southern pecan cultivar. HortScience 29(11):1290-1291.
15. Thompson, T.E. 1994. Chestnut, Filbert, Pecan, and Walnut. In: J.N. Cummins (ed.). Register of new fruit and nut varieties. HortScience 29(9):946, 955, 964.
16. Thompson, T.E. 1994. Mission and accomplishments of USDA-ARS pecan breeding and genetics unit. West. Pecan Conf. 28:239-240.
17. Thompson, T.E. 1994. The USDA pecan breeding program. Pecan Profitability Hdbk. pp. III 17-III 21.
18. Thompson, T.E. 1994. The USDA pecan breeding program. Proc. Third Natl. Mexico pecan Conf.
19. Thompson, T.E., Grauke, L.J., and Storey, B.J. 1994. Navaho pecan. Proc. Third Natl. Mexico Pecan Conf.
20. Grauke, L.J. and Thompson, T.E. 1995. Rootstock development. In: Sustaining pecan productivity into the 21st century (M.W. Smith. et al. Eds.) Second Natl. Pecan Workshop. USDA-ARS-195-3. pp. 167-172.
21. Grauke, L.J. and Thompson, T.E. 1995. Patterns of rootstock usage in the pecan industry. HortScience 30(3):431. (Abstract)
22. Storey, J.B., Grauke, L.J., Sistrunk, L., and Thompson, T.E. 1995. The influence of yield on fatty acid composition of pecan nuts. HortScience 30(3):432. (Abstract)
23. Thompson, T.E. and Grauke, L.J. 1995. Breeding improved pecan scion cultivars.In: Sustaining pecan productivity into the 21st century (M.W. Smith. et al. eds.) Second Natl. Pecan Workshop. USDA-ARS-1995-3. pp. 133-137.
24. Thompson, T.E., Grauke, L.J. and Storey, J.B. Navaho pecan. 1995. HortScience 30(1):156-157.
25. Thompson, T.E. Grauke, L.J., and Young, E.F. Jr. 1995. Pecan kernel color: Standards using Munsell color chips. HortScience 30(3):432. (Abstract)
26. Grauke, L.J. and Thompson, T.E. Variability in pecan flowering. Fruit Variety J. (In J. Review)
27. Thompson, T.E., Grauke, L.J., and Young, E.F. Jr. Pecan kernel color: Standards using the Munsell system of color notation. J. Amer. Soc. Hort. Sci. (In J. Review)
LJ Grauke , Research Horticulturist & CuratorUSDA-ARS Pecan Genetics
Route 2 Box 133
Somerville, TX 77879
tele: 409-272-1402
fax: 409-272-1401
e-mail:ljg@tamu.edu
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