Location: Crop Germplasm Research2010 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 2010, we evaluated more than 16,000 controlled-cross seedlings in the Basic Breeding Program (BBP). A new National Pecan Advanced Clone Testing System (NPACTS) test was established at College Station to test advanced USDA pecan clones identified in the BBP. Data from 21 other NPACTS tests in different regions of the U.S. pecan belt were added to master data bases to justify future pecan cultivar releases. The performance of two new pecan cultivars released in FY 2009 (Mandan and Apalachee) was monitored at several national evaluation sites for scab resistance and other characteristics. Work on the genetic control of high oleic fatty acid in pecan kernels was continued; development of productive new pecan types that are high in oleic acid will greatly enhance the nutritional value of pecan by contributing to lowered cholesterol levels in consumers. The goal of developing additional DNA markers related to scab resistance and other genetic traits is being pursued strategically through a newly developed cooperative effort with molecular researchers working on Juglans (walnut), a sister genus of Carya (pecan and hickory). The cooperator’s techniques as applied to Carya will allow evaluation of some 6000 genetic regions for similarity between the two genera. Existing genetic tools [known as simple sequence repeat (SSR) markers] were used to evaluate a subset of the pecan cultivar collection as well as a core of the provenance collection; the genetic variation seen across the range of pecan reflects as expected highly mobile pollen and relatively non-mobile seed. The controlled pecan population used for what is known as cross mapping for scab resistance was analyzed for physical (phenotypic) traits as related to observable expression of scab disease symptoms. Data will facilitate ongoing work to develop pecan types that are resistant or even immune to scab. A diverse group of pecan seedstocks was planted in 2009 into plots infected with the cotton root rot disease organism in an effort to identify sources of resistance to this devastating root problem. Mortality in the plantings was recorded in FY 2010. Both pecan and hickory seedstocks were established in plots infested with the root knot nematode as the first step in identifying nematode resistance in pecan germplasm; detailed assessments will be made in FY 2011. Efforts in FY 2010 to refine screening procedures for salt tolerance were not successful; approaches will be modified for work to be conducted in FY 2011. Salt tolerance work by the project thus far has shown that pecan seedstocks can be differentiated on the basis of chlorine (but not sodium) uptake. The traditionally preferred pecan seedstock (Riverside) for the western pecan-growing region was among the lowest in chlorine accumulation of all pecan types tested; but other seedstocks were identified that merit further testing for salt resistance.