1a. Objectives (from AD-416):
The long-term objective of this research is to develop and release high oleic peanut cultivars with superior oil chemistry, disease resistance, and agronomic performance. Over the next 5 years this research proposal will address the following objectives: Objective 1: Employ the most up-to-date genotyping, phenotyping, and marker-assisted selection strategies to develop and release superior peanut cultivars containing the most current disease resistance, agronomic, and quality trait genes, with emphasis on high yield, early maturity, oil, and seed quality traits. Subobjective 1A: Develop and release high-oleic, high-yielding runner, Virginia, and Spanish peanut cultivars with superior resistance to Sclerotinia blight, southern blight, and pod rot that are adapted for production in the SW United States. Subobjective 1B: Develop and map molecular markers associated with disease resistance in peanut that will aid in marker-assisted breeding. Objective 2: Improve existing methods and/or develop new methods to screen for resistance to Sclerotinia and southern blights and pod rot of peanut, and use these methods to identify useful resistance genes from the USDA peanut germplasm collection and other sources. Subobjective 2A: Define relationships between resistance to Sclerotinia and southern blights and response to oxalic acid, stem lignin content, and plant architecture characteristics. Subobjective 2B: Develop a reproducible greenhouse protocol for screening germplasm for resistance to pod rot.
1b. Approach (from AD-416):
Objective 1: Parental lines being used in such crosses include Arachis hypogaea L. cultivars, advanced breeding lines, and plant introductions (PIs) with demonstrated disease resistance and high oleic acid content. New and existing potential parent lines with high oleic acid content are continually tested in the greenhouse and field plots for resistance to Sclerotinia blight and southern blight and are readily available for use in the peanut breeding program. Included in our annual screening of germplasm for disease resistance are cultivars, breeding lines, and germplasm accessions. Also, collaborators include the curator of the U.S. peanut germplasm collection as well as other breeders who are continually evaluating accessions for value added traits. Molecular markers for Sclerotinia resistance will be identified and verified by phenotypic reaction. Advanced breeding lines will be tested in local, regional and national tests for agronomic performance before release as a variety. Objective 2: Response to oxalic acid, stem lignin content, and specific canopy architecture appear to be correlated with Sclerotinia resistance among cultivars of other legumes. We will determine if these traits are also useful for predicting resistance to Sclerotinia and southern blights in peanuts. Development of pod rot-resistant cultivars is significantly slowed by unpredictability of the disease occurring under field conditions. We will develop a reproducible greenhouse protocol for screening germplasm for resistance to pod rot by: 1) identifying and quantifying Pythium spp. and Rhizoctonia solani from Oklahoma and Texas fields with high incidences of pod rot using quantitative real-time PCR; and 2) evaluating symptoms in greenhouse-grown pods exposed to different inoculum levels of the three most common pod rot pathogens found in Oklahoma and Texas.
3. Progress Report:
This is a new project 6217-21220-007-00D (2/5/13 – 2/4/18). Additional details regarding this research can be found in the annual report for 6217-21220-006-00D, that expired on 2/4/13. In 2013, field trials for advanced breeding lines at all stages of development have been initiated, as well as state-wide variety trials and national Uniform Peanut Performance Tests. Laboratory and greenhouse testing of F1 and F2 hybrids with regard to oil chemistry and Sclerotinia blight resistance marker is complete, and selections for 2014 field trials have been made. All Recombinant Inbred Line (RIL) populations being developed for Sclerotinia blight resistance marker mapping have been advanced to the F6 population and are being readied for subset population increase. Sclerotinia blight and southern blight (also called white mold and stem rot) are two of the most important fungal diseases of peanut in the U.S. Studies evaluating oxalic acid as a potential resistance assay for Sclerotinia and southern blights were completed. Some significant differences in wilt symptoms were found among runner and Spanish cultivars, but differences did not consistently correspond to known levels of field resistance. These findings suggest the oxalic acid assay has limited potential, and that alternative assays should be studied for phenotyping breeding lines for Sclerotinia and southern blight resistance.