Mapping QTLs And Screening Germplasm For The Major Fatty Acid Components In Soybean Seeds

Soybean [Glycin Max (L.) Merr.] originated from China is the source of important protein and edible oil in the daily life. The soybean oil accounts for approximately 35%～40% of the market of the vegetable oil in the world.. The soybean oil is rich in some kinds of fatty acids such as oleic acid, linoleic acid and linolenic acid that are necessary matter for the human body growth and its quality is measured by the type of the fatty acid and proportion of the fatty acid component in the soybean oil . In China, the diversity of the soybean germplasm resource is abundant and the soybean quality trait exists in tremendous difference in different ecotypes. Analyzing the content of soybean fatty acid component variation in various yeas and ecotype regions and the correlation among fatty acid components, agronomic and quality traits play an important role in improving the quality of the soybean oil and soybean fatty acid breeding. A linkage group including 161 SSR markers constructed based on the RIL population derived from the cross LHD 2×NHZHD and mapped QTL for the fatty acids with method of CIMM(Composite Interval Mapping Method)in soybean has practical meaning for the molecular marker assistant breeding1. Consturction of the Rapid GC Methods for Determination of Fatty Acid ComponentsFive kinds of fatty acids components, including palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, were analyzed by the gas chromatograph (GC) method, and three of sample handling methods, including Soxhlet extraction, improved seed-methyl esterification and powder-methyl esterification methods, were compared in the five soybean varieties in order to reveal the differentiation among them. The results showed that the seed-methyl esterification method was simple and fast, which was suitable for the determination of single or half of seed in the low generation. The powder-methyl esterification method was relative accurate, which was good to the quick measurement of a great amount of soybean sample and can avoid decomposing the fatty acid components by the heating for long time. The Soxhlet extraction method has an advantage at the precision of analysis, but needs a great quantity of samples, the long time-consuming and lots of work. The test of precision showed that there was no significant different among the three kinds of methods, which demonstrated that both of the improved seed-methyl esterification and the powder-methyl esterification methods could be useful for determining the fatty acids components in soybean seeds.2. Analysis of the Major Fatty Acid Components in Soybean VarietiesNinety-one of the representative core soybean varieties from different ecotype regions were determined the fatty acid components by the GC method. The results showed that there were five fatty acid components, including palmitic acid (10.80%), stearic acid (4.24%), oleic acid (23.48%), linoleic acid (53.58%) and linolenic acid (7.79%) in soybean seeds. There were significant differences among years, ecotype regions and varieties on the fatty acid components. Based on the correlation coefficients among five fatty acid components, it showed that there was the significant negative correlation among oleic acid and palmitic acid, linoleic acid, linolenic acid (r = -0.32**,-0.85** and -0.46**) and a positive correlation between oleic acid and palmitic acid (r = 0.33**); A positive correlation between palmitic acid and linolenic acid (r = 0.31*) was presented; Otherwise, there was also a positive correlation between linoleic acid and linolenic acid (r = 0.28*) in this paper. In this experiment, two soybean varieties with high oleic acid and low linolenic acid content, cv. ChichengluhuangDou (oleic acid 33.2% and linolenic acid 5.7%) and cv. Mufeng1 (oleic acid 32.6% and linolenic acid 6.0%) and two soybean varieties with high linoleic acid and low linolenic acid, cv. Chasedou (linoleic acid 52.7% and linolenic acid 6.4%) and cv. Fangzhengmoshidou (linoleic acid 57.0% and linolenic acid 5.6%) were selected by the GC method for soybean fatty acid breeding.3. Performance of the Fatty acid Components and Agronomic Traits in RIL PopulationPerformance of the RIL population for fatty acids and agronomic traits in various years was different. Effective branches, pod number, lowest pod height and pods per plant were significantly affected by the environmental factors; However, the other traits less affected by the environmental factors. There was no significant difference for the contents of protein and oil in two yeas in RIL population. The analysis showed that the content of five fatty acid components were conformed to the normal distribution in 2009 and 2010, which demonstrated that the RIL population could be used as the mapping population for fatty acid components in soybean. The correlation among fatty acid components in the RIL population was reaching unanimity between two years, which indicated that although the effect by the environmental factor was presented, genetic factors still played an important factor affecting on the fatty acid components. Therefore, it was more important to focus on mapping QTLs for fatty acid component in soybean breeding.4. Construction of Soybean Linkage Map and Mapping QTL for Fatty Acid Component in Soybean SeedsThe RIL mapping population ( 100 lines, F5:7-8) derived from the cross LHD 2×NHZHD was established. The estimated linkage map, a total distance of 3572cM, was constructed with an average distance between markers of 22.19 cM using the 161 polymorphic SSR markers in the RIL population .A total of 13 QTLs associated with palmitic acid, stearic acid, oleic acid,linoleic acid and linolenic acid content were detected on the genetic linkage map in 2009. The QTLs were located at linkage group A1, M, G, O, K, B2 and N, which LOD value was2.62～12.7, and accounted for 5.6%～21.39% of the phenotypic variation. There was 1 QTL for Linoleic acid accounted for 11.08% of the phenotypic variation, located at linkage group N , which was apart from Satt530 for 0.7 cM; There were 2QTLs for Linolenic acid accounted for 18.98% and 21.39% of the phenotypic variation respectively , located at linkage group A1 and O .A total of 10 QTLs associated with palmitic acid, stearic acid, oleic acid, linoleic acid and linolenic acid content were detected on the genetic linkage map in 2010. The QTLs were located at linkage group A2, B2, C2, G, M and N, which LOD value was 2.58～10.81, and accounted for 4.09%～15.82% of the phenotypic variation. There was 1 QTL(qLA-1) for Linoleic acid accounted for 10.03% of the phenotypic variation, located at linkage group N ,which was apart from Satt530 for 0.02 cM; There were2 QTLs for linolenic acid which were totally accounted for 12.07%～14.33% of the phenotypic variation respectively , located at linkage group M. The QTLs(qPA-2 ,qSA-3 ,qLN-1) for palmitic acid, stearic acid and linoleic acid detected in 2009 were instant with the results in 2010.