Page Banner

United States Department of Agriculture

Agricultural Research Service

Research Project: PECAN GENETICS AND IMPROVEMENT
2013 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:
In FY 2013, project work accomplished several hundred controlled crosses in ongoing efforts to develop more productive and higher quality pecan cultivars. Work on evaluation of pecan germplasm for disease and insect resistance identified several promising leads; these will be pursued by additional, multi-year tests. Over the life of this project, about 4500 controlled cross progeny were developed in the scion (graft wood) and rootstock breeding programs. A biparental scab disease resistance population was planted at the College Station worksite with more than 350 individual plants. The population was evaluated for scab reaction, growth, and overall performance. More than 8,000 seedlings were evaluated in breeding nurseries. A new evaluation orchard of the National Pecan Advanced Clone Testing System (NPACTS) was established at the College Station worksite. Additional NPACTS orchards were cooperatively evaluated in several states. In work with academic cooperators, honeydew produced by aphids on pecan leaves was quantified using water-sensitive paper; the data showed there were 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. A diverse group of seedstocks was planted into plots infected with the cotton root rot fungus in work to identify sources of resistance to this serious root problem in commercial pecan orchards. Mortality due to the disease was confirmed and efforts at field screening were increased. Rootstock tests were established at the College Station worksite and with cooperators in New Mexico to determine the influence of seedstock on scion performance. Seedstocks representing broad genetic diversity were screened for nematode resistance; no sources of resistance were found. Three pecan cultivars (Apalachee, Mandan, and Lipan) were released to growers as the result of project work. Through application of modern molecular tools (SSR markers), Eclipse, a pecan patented by an Alabama pecan grower, was shown to be a project-developed controlled cross 1963-16-0182 (Mohawk x Starking Hardy Giant). This material will become the first germplasm release (as opposed to cultivar release) ever made by this project in its many decade history. This project expired in FY 2013 but was replaced by 6202-21000-035-00D which is expanding upon the work of the precursor project.


Review Publications
Honaker, J., Skrivanek, S., Lopez, J., Martin, D.E., Lombardini, L., Grauke, L.J., Harris, M. 2013. Blackmargined aphid (Monellia caryella (Fitch); Hemiptera: Aphididae) honeydew production in pecan (Carya illinoinesis (Koch)) and implications for managing the pecan aphid complex in Texas. Southwestern Entomologist. 38:19-32.

Last Modified: 10/30/2014
Footer Content Back to Top of Page