Peanut is an oilseed crop whose seeds contain ~50% oil. Oleic and linoleic fatty acids comprise ~80% of peanut oil. Oleic acid is an eighteen carbon chain fatty acid with one double bond at the C9 position. The microsomal enzyme delta-12-desaturase catalyzes the addition of a second double bond at C12 to convert oleic acid to linoleic. Normally the O/L ratio in peanut cultivars is 3:1. It has been shown that oleic acid can reduce the risk of heart disease by decreasing LDL synthesis. A high O/L ratio also increases the shelf life of peanut products. F435, a high oleic acid spontaneous mutant with an O/L ratio of 35:1, was identified in 1987 (Norden et al. 1987, Peanut Sci 14:7). Two delta-12-desaturases (ahFAD2A and ahFAD2B) also were discovered in peanut (Jung et al. 2000).
Dysfunction of both genes is required to produce a high O/L peanut. Earlier studies found two models of segregation among progenies of high oleic × normal oleic parents, i.e., 3:1 and 15:1. These data suggested that one of the genes already is mutated in some normal O/L cultivars, a hypothesis that was tested using a cleaved amplified polymorphic sequence (CAPS) marker to track a G448A mutation in the ahFAD2A allele (Chu et al. 2007).
We further screened the mini-core collection of U.S. peanut germplasm and found 31.6% of the accessions carry this mutation. In addition to the F435 spontaneous mutation, another high oleic mutant line Flavorunner was induced by diethyl sulfate mutagenesis resulting in the insertion of a MITE (miniature inverted transposable element) in the coding region of ahFAD2B (Patel et al. 2004).
Variation of the O/L ratio in Flavorunner has been observed during commercial production. We are currently investigating whether there is any genetic basis for this variation in order to develop a more stable line for high O/L.