Partial Dominance , Pleiotropism , and Epistasis in the Inheritance of the High - Oleate Trait in Peanut

Abstract

Earlier reports of the high-oleate (low-linoleate) trait in peanut (Arachis hypogaea L.) indicated that it was controlled by completely dominant gene action. However, linoleate content intermediate to that in lowand normal-linoleate seeds was found among progeny when the trait was backcrossed into five virginia-type cultivars, suggesting partial dominance of the gene controlling the trait. Although BC1F2 results were inconsistent across recurrent parents, data from the BC2F2 and BC3F2 populations of all crosses conformed to the 1:2:1 ratio expected under partial dominance. Quantitative analysis showed that fatty acid levels were affected by the background genotypes of the recurrent parents, suggesting that there are other genes that influence fatty acid. The ol gene exhibited pleiotropism by influencing not only oleate and linoleate, but also levels of palmitate, total C18 fatty acids, gadoleate, and total saturated fatty acids. The effects of the ol gene interacted with background genotype, particularly with the additive genetic contrast, suggesting epistasis in the general sense. Progeny testing of 59 putatively heterozygous and 41 homozygous normal BC2F2 plants indicated that the two genotypes could be distinguished accurately on the basis of linoleate level, suggesting that the ol gene can be moved by backcrossing using techniques appropriate for a dominant trait rather than a recessive trait. THE HIGH-OLEATE TRAIT (low-linoleate) of peanut results in longer shelf-life for peanuts and peanut products and is therefore of great interest to the U.S. peanut industry (Ahmed and Young, 1982). In most U.S. germplasm, the trait is controlled by two duplicate genes, ol1 and ol2 (Moore and Knauft, 1989), one of which is common in U.S. runnerand virginia-type peanut cultivars as evidenced by the high frequency of monogenic segregation ratios observed in crosses of these types of cultivars with F435, the source of the trait (Knauft et al., 1993; Isleib et al., 1996). Earlier reports of the higholeate trait indicated that the rare gene controlling the trait (hereafter called ol) exhibited complete recessivity (Moore andKnauft, 1989; Knauft et al., 1993; Isleib et al., 1996). Different patterns of inheritance indicative of three-gene control with dominant and recessive epistasis were detected in crosses of F435 with parents of the spanishmarket type (López et al., 2001, 2002). This work also suggested quantitative inheritance beyond the genes with large influence on the trait. The peanut breeding program at N.C. State University (NCSU) among others has been backcrossing the high-oleate trait into several different cultivars and breeding lines. At NCSU, the initial cycle of selection followed several generations of single-seed descent designed to increase the probability of recovering higholeate plants from populations of limited size. The fatty acid assay used in the first cycle required that oil be extracted from a sample of several seeds (Isleib et al., 1996). Subsequent cycles of backcrossing and selection have been based on data collected from small cotyledonary samples from individual F2 seeds as described by Zeile et al. (1993). In the three cycles of backcrossing completed since the initial cycle of selection, it was observed that although the high-oleate/low-linoleate seeds were readily identified by having linoleate values below 70 g kg of total fatty acids, there was a broad range of values for linoleate and oleate in the non–high-oleic “normal” plants. The objectives of this study were to determine whether the distributions of fatty acid contents conformed to simple dominance, to quantify the effect of the rare ol gene on oleate, linoleate, and other fatty acids, and to determine whether the effect of the ol gene was uniform across background genotypes. MATERIALS AND METHODS The initial crosses of large-seeded virginia-type cultivars NC 7 (Wynne et al., 1979), NC 9 (Wynne et al., 1986), NC 10C (Wynne et al., 1991a), NC-V 11 (Wynne et al., 1991b), and VA-C 92R (Mozingo et al., 1994) to F435 were made in 1990 as described by Isleib et al. (1996). The first backcross to each of the five cultivars was made in the summer of 1994 using F4:5 lines identified with the high-oleate trait as nonrecurrent parents. BC1F1 plants were grown in the greenhouse during the winter of 1994–1995. BC1F2 seeds were harvested and analyzed for fatty acid content as described by Zeile et al. (1993). A plug of cotyledonary tissue was removed from the seed by inserting a sharpened ball inflator needle into the seed perpendicular to the plane of the lumen. The plug was placed in a vial. The lipids in the plug was extracted for 8 h in 0.5 mL of chloroform/hexanes/methanol (8:5:2, V/V/V). Fatty acid methyl ester derivatives were made by transesterification using sodium methoxide. Fatty acids were quantified using an HP 5890 Series II GC equipped with dual AT-Silar (Alltech Assocs., Deerfield, IL) columns (30 m by 0.53 mm i.d.) and flame ionization detectors (FIDs). The carrier (He) flow was 5 mL min, temperatures were 2508C for the injectors, 2008C for the oven, and 2758C for the FIDs. Retention times and response factors for the eight peaks of interest were calibrated against authentic standards (Supelco, Bellefonte, PA). In addition to the concentrations of individual fatty acids, sums were computed for total C18 fatty acids, that is, the total of the concentrations of stearate, oleate, and linoleate; the total satuT.G. Isleib, Dep. of Crop Science, N.C. State Univ., Raleigh, NC 27695-7629; R.F. Wilson, USDA-ARS National Program Staff, 5601 Sunnyside Ave., GWCC-BLTSVL, Beltsville, MD 20705; and W.P. Novitzky, USDA-ARS Soybean and Biological Nitrogen Fixation Group, N.C. State University, Raleigh, NC 27695-7620. This project was supported in part by a grant from the North Carolina Peanut Growers Association. Received 14 Sept. 2005. *Corresponding author (tom_isleib@ncsu.edu). Published in Crop Sci. 46:1331–1335 (2006). Crop Breeding & Genetics doi:10.2135/cropsci2005.09-0313 a Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA Abbreviations: O/L ratio, ratio of the concentration of oleate to linoleate. R e p ro d u c e d fr o m C ro p S c ie n c e . P u b lis h e d b y C ro p S c ie n c e S o c ie ty o f A m e ri c a . A ll c o p y ri g h ts re s e rv e d . 1331 Published online April 25, 2006

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@inproceedings{Novitzky2006PartialD, title={Partial Dominance , Pleiotropism , and Epistasis in the Inheritance of the High - Oleate Trait in Peanut}, author={William P. Novitzky}, year={2006} }