Location: Peanut and Small Grains Research Unit
2020 Annual Report
Objectives
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: Identify new sources of resistance to industry-relevant peanut pathogens, and use improved marker assisted selection (MAS) methods and QTL analyses to incorporate those genes into existing and new peanut cultivars.
Subobjective 1A: Phenotype existing recombinant-inbred line (RIL) populations and the minicore collection from the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) for Sclerotinia blight and/or early leaf spot resistance and the U.S. mini-core germplasm collection for southern blight resistance in field trials.
Subobjective 1B: Genotype existing RIL populations and the U.S. and ICRISAT mini-core germplasm collections using a 48K SNP micro-array chip for tetraploid peanut; genotype existing RIL populations with SSR markers associated with Sclerotinia blight resistance. Analyze phenotypic and genotypic data collected in Subobjectives 1A and 1B to identify possible QTL for disease resistance and design molecular markers to be used in MAS breeding.
OBJECTIVE 2: Develop improved peanut varieties with superior genetic improvements and agronomic and plant health traits, including disease resistance, early maturity, elevated yield, oil, drought tolerance, and seed quality.
Subobjective 2A: Develop and release elite high-oleic, high-yielding, and/or early maturing runner, virginia, and spanish peanut cultivars with superior resistance to Sclerotinia blight, southern blight, drought and/or pod rot that are adapted for production in the SW United States.
Subobjective 2B: Phenotype U.S. peanut mini-core for drought tolerance and plant canopy architecture.
Subobjective 2C: Determine effects of cover crop mixtures and rotation crops on Pythium pod rot in susceptible commercial cultivars.
OBJECTIVE 3: Discover and characterize new genes from cultivated and wild Arachis species in the U.S. National Peanut Germplasm Collection for resistance to existing and emerging diseases, such as peanut smut.
Subobjective 3A: Phenotype the U.S. mini-core collection and other germplasm for resistance to peanut smut and develop new methodologies for high-throughput screening of peanut pods for the presence of peanut smut.
Subobjective 3B: Conduct crossing experiments between smut resistant germplasm and U.S. peanut cultivars to develop and release new smut resistant peanut varieties suitable for production in the Southwestern U.S.
Subobjective 3C: Phenotype wild Arachis species for resistance to Sclerotium rolfsii.
Approach
Objective 1: Two RIL populations (CAP and Sclerotinia marker) and germplasm collections will be evaluated for Sclerotinia blight and/or early leaf spot resistance in separate field experiments for three years. The U.S. mini core collection will also be evaluated for Sc. rolfsii resistance for three years. Genotyping of RIL populations will also be conducted using the Axiom Arachis Custom Array for tetraploid peanut, covering 48K SNPs as well as SSR markers identified as flanking the region reported as a possible QTL for Sclerotinia blight resistance. Phenotype and genotypic data will be combined for quantitative trait loci (QTL) mapping. Multiple methods for QTL detection will be implemented including interval mapping, and composite interval mapping. Phenotypic coefficients of variation and heritabilities also will be estimated. Genetic maps will be constructed.
Objective 2: Parental lines being used in such crosses include Arachis hypogaea L. cultivars, advanced breeding lines, and plant introductions (PIs) with demonstrated disease resistance and/or drought tolerance. For each cross performed, a modified bulk selection breeding method will be used. Breeding lines will be advanced annually, screening for disease resistance, oil composition, and agronomic performance. F7 generation ines will be entered into advance performance trials such as the Oklahoma Peanut Variety Tests, advanced line disease resistance tests and the national Uniform Peanut Performance tests and tested by the USDA ARS Peanut Market Qualtiy lab before release. The U.S. mini-core collection will be evaulated for drough tolerance and canopy architecture by monitoring performance under water deficit irrigation and collecting data on leaf wilting, paraheliotropism, normalized difference vegetation index, upper canopy temperature, flower abundance, SPAD chlorophyll stability, and descriptive canopy traits. The canopy traits will be collected using a LiDAR camera. A four-year experiment to determine the effect of cover crops on pod rot persistence will be conducted. Experimental treatments will include combinations of three winter cover crops and two rotation crop sequences.
Objective 3: The U.S. mini-core collection and other selected genotypes will be evaluated for at least 3 years in T. frezzii-infested fields in Manfredi, Argentina. To incorporate newly found smut resistance into adapted peanut lines, crossing and early generation breeding line and cultivar development will be conducted. Prototypes of a new smut screening technology will be developed and shipped to Argentina and test. Seeds will be removed from pods and replaced with talcum powder to simulate T. frezzii spores. Acoustic measurements will be taken from twenty pods of each treatment. To discover new southern blight resistance among wild Arachis species, experimental treatments will include a total of 62 accessions representing 26 species of Arachis, in addition to the susceptible cultivar Florunner.
Progress Report
For Subobjective 1A, progress was made by continuing to increase seed from single-plant selections of the mini-core collection from the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT). The seed will be used to evaluate early leaf spot and pod rot resistance in the field, and each accession will be genotyped to identify markers for disease resistance. For Subobjective 1B, simple sequence repeat (SSR) genotyping of recombinant inbred lines (RILs) was completed. Correlation of genotypic and Sclerotinia blight resistance phenotypic data was delayed by one year due to an early freeze in October of 2019 that halted all phenotyping efforts.
For Subobjective 2A, field evaluation of all breeding lines was completed. Breeding lines were identified for all generations that will be moved forward to further testing and advanced line performance trials. Greenhouse testing of F1 and F2 hybrids was completed and selections were made to advance to field testing. Eleven (11) advanced breeding lines (nine runner and two Spanish) were evaluated for resistance to Sclerotinia blight and pod rot. For Subobjective 2B, the third and last year of field experiments were completed for the multi-state project phenotyping the U.S. mini core for drought resistance. Data were collected manually and with high-throughput methods such as unmanned aerial vehicle (UAV) and ground-based platforms.
For Subobjective 3A, year 2 of phenotyping for resistance to peanut smut was successful in confirming resistance seen in year 1 for 27/35 (77%) of the entries retained for further testing. In addition, 17 new entries were identified as having smut resistance, with 12 of those entries demonstrating 1% or less disease incidence. A total of 44 entries tested in 2018-2019 were retained for testing again in 2019-2020. Also, for Subobjective 3A, the design for an X-ray system able to efficiently screen pods for peanut smut was completed. For Subobjective 3C, experiments evaluating 18 accessions of 15 wild Arachis species for resistance to Athelia rolfsii were completed. These experiments identified an accession of Arachis microsperma with resistance comparable to the most resistant cultivated peanuts.
Accomplishments
1. Disease-resistant wild peanut for pre-breeding. Cultivated peanut, even those collected from peanut's center of origin in South America, possess little genetic variation. In contrast, many wild peanut species have high levels of genetic diversity, and importantly, resistance to various biotic stressors. ARS researchers in Stillwater, Oklahoma, and Griffin, Georgia, identified an accession of Arachis microsperma with high resistance to the fungus Athelia rolfsii, the most damaging soilborne pathogen of peanut in the United States. Because Arachis microsperma has an "A" genome like cultivated peanut, resistance genes can be more easily transferred from this species using traditional breeding techniques. In Georgia alone, an estimated $91.4 million was lost in yield and control costs from Athelia rolfsii in 2017. Disease-resistant peanut cultivars developed from this accession would save growers millions of dollars and improve environmental and health impacts of peanut production by reducing fungicide applications.
Review Publications
Bennett, R. 2020. Growth chamber assay for evaluating resistance to Athelia rolfsii. Peanut Science. (47)1:25-32. https://doi.org/10.3146/PS19-12.1.
Bennett, R.S., Chamberlin, K.D. 2021. Resistance to Athelia rolfsii and web blotch in the U.S. Mini-core Collection. Peanut Science. 47(1):17-24. https://doi.org/10.3146/PS19-18.1.
Chamberlin, K.D., Baldessari, J., Mamani, E.M., Moreno, M.V. 2020. Screening of the Argentinean INTA peanut core collection with a molecular marker associated with resistance to Sclerotinia minor Jaggar. Peanut Science. (47)1:9-16. https://doi.org/10.3146/PS19-15.1.
