Abstract A sunflower mutant, CAS-3, with about 25% stearic acid (C18:0) in the seed oil was recently isolated after a chemical-mutagen treatment of RDF-1-532 seeds (8% C18:0). To study the inheritance of the high C18:0 content, CAS-3 was reciprocally crossed to RDF-1–532 and HA-89 (5% C18:0). Significant reciprocal-cross dif- ferences were found in one of the two crosses, indicating possible maternal effects. In the CAS-3 and RDF-1–532 crosses, the segregation patterns of the F 1 , BC 1 , and F 2 populations fitted a one-locus (designated Es1) model with two alleles (Es1, es1) and with partial dominance of low over high C18:0 content. Segregation patterns in the CAS-3 and HA-89 crosses indicated the presence of a second independent locus (designated Es2) with two al- leles (Es2, es2), also with partial dominance of low over high C18:0 content. From these results, the proposed ge- notypes (C18:0 content) of each parent were as follows: CAS-3 (25.0% C18:0) =es1es1es2es2; RDF-1–532 (8.0% C18:0) =Es1Es1es2es2; and HA-89 (4.6% C18:0) =Es1Es1Es2Es2. The relationship between the proposed genotypes and their C18:0 content indicates that the Es1 locus has a greater effect on the C18:0 content than the Es2 locus. Apparently, the mutagenic treatment caused a mutation of Es1 to es1 in RDF-1–532. Key words Helianthus annuus · Sunflower mutant · Stearic acid · Oil quality · Genetic control Introduction The quality of sunflower seed oil, both for food and non- food applications, is mainly determined by its constitu- ent fatty acids. Standard sunflower oil contains approxi- mately 11% of the saturated palmitic (C16:0) and stearic (C18:0) fatty acids, the rest being the unsaturated oleic (C18:1) and linoleic (C18:2) acids (Dorrell and Vick 1997). Because of this fatty acid composition, sunflower oil is liquid at room temperature. The use of mutagenesis produced sunflower lines with higher concentrations of C16:0 (>25%; Ivanov et al. 1988; Osorio et al. 1995; Fernández-Martínez et al. 1997) and C18:0 (>22%; Osorio et al. 1995). The higher saturated level of the oils from these mutants will in- crease the utility and improve the quality of sunflower oil for specific edible purposes. First, this type of oil re- quires no chemical transformations such as hydrogena- tion or transesterification in order to obtain solid or semi-solid fats. Such oil-transformations have been relat- ed to cardiovascular diseases (Kritchevsky et al. 1995; Ascherio and Willet 1997). Second, the oil from these mutants will show higher stability than the oil from cur- rently available cultivars, as described in high C18:0 lines in soybean (Lui and White 1992), and will find many applications in the field of solid and semi-solid fats, such as the manufacture of margarine, shortenings for baking, or fats for deep frying. A requisite for the commercial use of the new oils is the incorporation of the modified biosynthetic pathway into sunflower hybrids with a good agronomic perfor- mance. This requires previous knowledge on the genetic behavior of the trait. Previous studies on the genetics of the seed-oil quality in sunflower have been focused on the study of the high C18:1 trait. These studies demon- strated that the genetic control of the high C18:1 trait is mainly gametophytic, dominant, and determined by a low number of genes (Fick 1984; Urie 1985; Miller et al. 1987; Fernández-Martínez et al. 1989). Such characteris- tics have permitted the rapid development of sunflower hybrids with a very high C18:1 content (90%) (Fern- Communicated by P.L. Pfahler B. Pérez-Vich · J.M. Fernández-Martínez ( ✉ ) Instituto de Agricultura Sostenible, CSIC, Apartado 4084, E-14080 Córdoba, Spain e-mail: cs9femaj@uco.es Fax: +34 957 499252 R. Garcés Instituto de la Grasa, CSIC, Apartado 1078, E-41080 Sevilla, Spain Theor Appl Genet (1999) 99:663–669 © Springer-Verlag 1999 B. Pérez-Vich · R. Garcés · J.M. Fernández-Martínez Genetic control of high stearic acid content in the seed oil of the sunflower mutant CAS-3 Received: 20 September 1998 / Accepted: 1 February 1999