1a. Objectives (from AD-416)
The long-term objective of this project is to improve the genetics of peanut for disease resistance and the oleic acid content of oil. Objective 1. Develop peanut germplasm that is high-oleic in nature with improved resistance to Sclerotinia blight and southern blight. Objective 2. Develop molecular markers for peanut associated with resistance to Sclerotinia blight and southern blight. Objective 3. Develop improved methodology to characterize the reaction of Sclerotinia minor and Sclerotium rolfsii on inoculated peanut germplasm and breeding lines under greenhouse conditions.
1b. Approach (from AD-416)
Parental lines being used in such crosses include Arachis hypogaea L. cultivars, advanced breeding lines, and plant introductions (PIs) with demonstrated Sclerotinia 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 phonotypic reaction.
3. Progress Report
The long-term objective of this project is to improve the genetics of peanut for disease resistance and the oleic acid content of oil. Substantial progress has been made toward that end. Advanced breeding lines with improved genetics for the high oleic trait as well as resistance to Sclerotinia blight are now in their second year of performance trials. Analysis of the results of year 2 trials allowed the identification of breeding lines for further advancement, and also resulted in the removal of poor performing lines from the program. Additionally, we are using a newly developed non-destructive technique using capillary electrophoresis to determine the concentration of oleic and linoleic acid in a single peanut seed. This technique has allowed rapid screening of early generation breeding lines for those individual seed possessing the desired high oleic acid trait. Identification of new high oleic Virginia market-type lines with resistance to Sclerotinia blight has resulted from this process and allowed those lines to enter advanced trials earlier than expected. Progress was also made toward placing the molecular marker for Sclerotinia blight resistance on the tetraploid peanut map. Genotypic and phenotypic data from one mapping population was gathered and another population is currently being generated. Due to an unfortunate natural disaster, much of the original population was lost. The marker is also being used to examine members of the ICRISAT Mini-Core Collection for possible new sources of resistance to Sclerotinia blight. Also, it was determined that a post inoculation high relative humidity (98-100%) of 24 hours is needed to attain 65% infection of peanut with Sclerotinia minor under greenhouse conditions.
1. New technique expedites the release of high oleic peanut varieties. Peanut varieties with high oleic/linoleic acid ratios have become preferred by the peanut industry due to their increased shelf life and improved health benefits. Many peanut breeding programs are trying to incorporate the high oleic trait into new and improved varieties and are in need of diagnostic tools to track its inheritance early in development and at the single seed level. Traditionally, gas chromatography (GC) has been used to accurately determine the properties of peanut oil, but this method generally requires modification of oil after extraction and possible destruction of the seed sample. In this study, a non-destructive technique (capillary electrophoresis or CE) was used to determine the oil content of a single peanut seed. Over 100 samples were processed, covering runner, Spanish and Virginia market types. Results showed that CE and GC were 100% in agreement in determining whether a peanut seed is "high-oleic" or "normal oleic" in oil content. Results from this study validate the use of CE as a diagnostic tool for breeding programs to identify individual high oleic peanut seed for further testing and development. This accomplishment is important because it has allowed for improved efficiency in the breeding of peanut for high oleic acid content.
Chamberlin, K.D., Melouk, H.A., Payton, M.E. 2010. Evaluation of the U.S. peanut mini core collection using a molecular marker for resistance to Sclerotinia minor Jagger. Euphytica. 172:109-115.