Location: Crop Germplasm Research2015 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: Develop new pecan scion cultivars with high yield, superior nut quality, and improved resistance to diseases and insects. Focus will be on early nut maturity to reduce impact of alternate bearing and improved resistance to pecan scab. Sub-objective 1A: Develop high yielding pecan scion cultivars with early nut maturity, improved nut quality, and superior disease and insect resistance. Sub-objective 1B: Elucidate the genetic control of key horticultural traits in pecan utilizing appropriate qualitative and quantitative techniques. Sub-objective 1C: Characterize kernel composition found in native pecans across the species range. Objective 2: Develop superior rootstocks with outstanding vigor and site adaptation for all pecan growing regions. Sub-objective 2A: Quantify heterosis in pecan. Sub-objective 2B: Screen diverse seedling rootstocks for resistance to the root knot nematode. Sub-objective 2C: Refine recognition of rootstock effects on phenology and nutrient accumulation, impacting regional deployment. Objective 3: Develop genetic markers for use in genotyping diverse Carya breeding lines. Sub-objective 3A: Develop scaffold framework for sequence alignment. Sub-objective 3B: Use Restriction-site Associated DNA sequencing (RADseq) techniques to conduct phylogeographic analysis on populations of native pecans.
1b. Approach (from AD-416):
Research objectives will be met by basic genetic research and by an intensive cultivar and rootstock selection program. Phenotypic breeding techniques, supplemented with molecular tools, will be used to develop and release new pecan scion cultivars with high yield and quality, 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 2015 work, project objectives to develop new pecan scion cultivars with high yield and superior nut quality were addressed through creation of a series of controlled crosses (Objective 1). In efforts to meet project objectives of developing superior rootstocks with outstanding vigor and site adaptation (Objective 2), novel rootstock crosses were made based on results of flow cytometry evaluations of germplasm made in the sister project (3091-21000-036-00D). Scab disease screening procedures (Objective 1) were revised by development of a high intensity screening nursery, and by attempts to isolate, culture, and inoculate with scab. Scab screening of controlled cross progeny seedlings was conducted, and resistant seedlings were identified and will be subjected to additional testing. Greenhouse plantings of geographically diverse seed stocks of pecan were screened for tolerance to salinity. More than 2700 seedlings in a cotton root rot screening nursery in Uvalde, Texas, were monitored for phenology (site/climate/etc. adaptation) in cooperation with cooperators at Texas A&M AgriLife Research. An orchard of diverse seedling pecan rootstocks was propagated by grafting and budding. In efforts to develop genetic markers for use in genotyping diverse Carya breeding lines (Objective 3), genetic information in the pecan draft genome sequence (created by cooperators at a major genome sequencing center) was analyzed for informative leads to guide further genetic research. Genetic tools known as single nucleotide polymorphic (SNP) DNA markers for Carya were obtained from the Juglans (walnut) SNP chip in cooperation with colleagues at a cooperating genome resources center.
Grauke, L.J., Klein, R.R., Grusak, M.A., Klein, P. 2015. The forest and the trees: Applications for molecular markers in the Pecan Breeding Program. Acta Horticulturae. 1070:109-126.
Jenkins, J., Wilson, B., Grimwood, J., Schmutz, J., Grauke, L.J. 2015. Towards a reference pecan genome sequence. Acta Horticulturae. 1070:101-108.