Submitted to: Peanut Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/6/2011
Publication Date: 6/1/2011
Citation: Barkley, N.L., Chamberlin, K.D., Wang, M.L., Pittman, R.N. 2011. Genotyping and fatty acid composition analysis in segregating peanut (Arachis hypogaea L.) populations. Peanut Science. 38:11-19. Interpretive Summary: Dietary fats are essential to humans because they supply energy, help regulate body temperature, and carry fat soluble vitamins. Fatty acids are characterized by the number of carbon and hydrogen atoms along with the absence or presence of double bonds in the hydrocarbon chain. Saturated fatty acids contain no double bonds; whereas, unsaturated fatty acids have at least one or multiple double bonds. Due to the differences in chemical structure of the many different fatty acids, they all have unique properties. For example, oleic acid has a single double bond in its hydrocarbon chain which makes this fatty acid very stable. On the other hand, linoleic acid which has two double bonds in the hydrocarbon chain tends to break down which ultimately produces off flavors in oil or seeds containing oil. Therefore, oils or edible seeds containing oils are more stable if they are composed of a high amount of oleic acid and low amounts of linoleic acid. Peanut seeds and peanut oil are comprised of both oleic and linoleic fatty acids. The flavor and quality of the seed or the extracted oil is dependent on the fatty acids because a high amount of oleic acid in a peanut seed provides increased shelf life over peanuts with low levels of oleic. Traditionally, oleic acid content is measured from ground up seed using an analytical chemistry method known as gas chromatography. Previous molecular analysis however has demonstrated that two key mutations in ahFAD2 genes are required to produce high oleic peanuts. These mutations can be identified rapidly by extracting DNA and assessing if the mutations are present or not. The advantage of the molecular assay is that high oleic lines can be identified by using leaf tissue as opposed to seed slices. Thus, the goal of this work was to employ a molecular assay to rapidly assess breeding lines for specific mutations in a gene known as ahFAD2B in conjunction with evaluating fatty acid data to determine the affect of different alleles on the level of oleic acid accumulation in peanut populations.
Technical Abstract: Oleic acid (C18:1), a monounsaturated omega-9 fatty acid is an important seed quality trait in peanuts (Arachis hypogaea L.) because it provides improved flavor, enhanced fatty acid composition, a beneficial effect on human health, and increased shelf life for stored food products. Consequently, an emphasis has been placed on breeding peanuts with high levels of oleic acid and low levels of linoleic acid (C18:2), a polyunsaturated, omega-6 fatty acid. Therefore, crosses were prepared between high oleic and normal peanut lines to develop segregating F2 populations. In order to rapidly identify the trait of interest and expedite breeding efficiency, a genotyping assay was developed to track the inheritance of ahFAD2B alleles which influence oleic acid accumulation. Total fatty acid composition and the ahFAD2B genotype were determined in the parents and progeny. The oleic to linoleic ratio (O/L) varied from 0.85 to 30.30 in the F2 progeny. Comparing the mean oleic acid values from the three genotypic classes (Ol2Ol2, Ol2ol2, and ol2ol2) detected in each population demonstrated that the homozygous recessive genotype generally contained a higher level of oleic acid than the heterozygous or the homozygous dominant genotype. Statistical analysis demonstrated that oleic acid was negatively correlated with linoleic and palmitic acid, but was positively correlated with gadoleic and lignoceric fatty acids. This suggests that modifier genes may influence fatty acid composition. Principally, integration of genotyping and phenotyping data from segregating populations provided valuable insights on the genetic factors controlling total fatty acid composition.