| The increase of oleic acid content in soybean [Glycine max (L.) Merr.] oil improves its nutritional value and oxidative stability therefore, the incorporation of the high oleate trait in soybean germplasm is required for the continued commercial success of soybean oil. Little is known, however, about the response to selection for higher oleate content, which is dependent on its heritability in breeding populations, and the correlated responses of other fatty acids and agronomic traits to selection for oleate content, which depends on their genetic correlations with oleate. Furthermore, the lack of knowledge on the genetic factors underlying oleate variation in soybean oilseeds hampers the use of marker assisted selection for high oleate content in soybean breeding programs. Three soybean populations segregating for major and minor oleate genes, which were grown in replicated multi-environment trials, were studied in order to shed light on the research questions above.The results of this study suggested that oleate heritability was sufficiently high that early generation selection can be effective when practiced on unreplicated lines grown at a single environment. Moreover, this study indicated that selection for higher oleate content will result in lower linoleate, linolenate and palmitate content in soybean oil. Also, the significant negative correlation between oleate content and yield implied that the development of high oleate germplasm may be hindered by lower yields. The isoforms of the FAD2-1 and FAD2-2 genes, which encode the microsomal o-6 desaturase enzymes that catalyze the desaturation of oleic acid to linoleic acid during fatty acid biosynthesis, were mapped in order to investigate their cosegregation with the oleate quantitative trait loci (QTLs) identified. The FAD2-1A and FAD2-1B isoforms mapped on linkage groups O and I, respectively, while the closely linked FAD2-2A and FAD2-2B isoforms mapped on linkage group L of soybean genome. An oleate QTL with moderate effects was reported in the proximity of FAD2-1B isoform on linkage group I. Also, an oleate QTL with moderate effects was detected on linkage group F, which interacted epistatically with the QTL on linkage group I. In conclusion, no major oleate QTLs were identified and the FAD2-1A, FAD2-1B and FAD2-2B isoforms did not encode for the major oleate genes that contributed to the elevated oleic acid content of the experimental lines used in this study. |
