| Soybean [Glycine max (L.) Merr.], originated from China, is one of the most important sources of vegetable protein and edible oil world-widely. Soybean oil accounts for about 35% of the world's vegetable oil market. Soybean oil is rich with essential fatty acids for human bodies, the quality of which depends on the type and magnitude of fatty acid composition. There is a great genetic diversity of soybean germplasms, with them widely distributing in our country. Big differences in quality property of soybeans exist among eco- regions in China. Investigating variation and inheritance mechanism of fat and fatty acid composition of soybeans from different eco-regions is of great significance to soybean fat quality breeding, and to the improvement of soybean quality property.Several studies have been done on ecological characteristic, geographical distribution, and inheritance mechanism of soybean fatty traits (Fatty traits described in this paper were referred to fat content and fatty acid composition in soybean seed), and some results obtained. But the results were mainly involved in protein and fat contents of soybeans, and less concern was on fatty acid composition. What's more, materials used in experiments were mostly from local regions, resulting in the limitation of reference to soybean breeding. Nowadays in soybean fat quality breeding, concern is mainly focused on the variations of soybean fatty traits from special eco-regions. The main objectives of this study were: (1) probing the variation of fat and fatty acid composition of soybeans from different eco-regions in China; (2) revealing inheritance mechanism of fatty traits of soybeans; (3) mapping QTLs of fatty trait related genes. The results of this study will be helpful for soybean fat quality breeding.Cultivated and wild soybeans from different eco-regions were sampled and used in this experiment carried out in 2002 year in Nanjing. Principal component analysis method was used to investigate variations of soybean fat related traits from different eco-regions classified by Junyi Gai (2001). The results were as follows: (1) From nation-widely, the average contents of fat and oleic acid of cultivated soybean(G.max)(17.21% and 23.25%, respectively) were significantly higher than that of wild soybean(G.soja) (10.99% and 15.50%, respectively) ; while the average content of linolenic acid (8.00%) of G. max was significantly lower than that of G.soja (12.23%). The average content of linoleic acid of G. max (53.53%) was a little lower than that of G. soja(56.10%).There was no big differnce in saturated fatty acid content between G.max and G.soja. (2) In the same eco-region of G.max, large variations could be found among fat, oleic, linolenic and stearic acids, with C.V. of more than10% ,but only small variations among palmitic and linoleic acids with C.V. of less than 10% ;small variations of fat and fatty acid contents existed between different eco-regions. The case was true of. G. soja. (3) The results of principal component analysis showed that variation type and direction of fat and fatty acid, explained mainly by fat and unsaturated fatty acid contents both in wild and cultivated soybeans, were different among eco-regions. In a word, The average contents of fat and oleic acid of G. max were significantly higher than that of G. soja; while the average content of linolenic acid of G. max was significantly lower than that of G.soja. The average content of linoleic acid of G.max was a little lower than that of G. soja. There was no big difference in saturated fatty acid content between G. max and G.soja. Large variations of soybean fatty traits existed in every eco-region; and variations of inter-eco-region were not definitely bigger than that of intra-eco-region. Variation type and direction of fat and fatty acid composition were different among eco-regions, both in wild and cultivated soybeans; fat and unsaturated fatty acid composition contents contributed mainly to the total variations, while saturated fatty acid composition explained a small portion. Soybean germplasms, including G.soja and G.max, with quality fatty trait of interest, were selected.Soybean germplasms, Essex and ZDD2315, with big differences in agronomic and fatty traits were chosen from general screenings and used to reveal the genetic mechanism of fat and fatty acid composition content in soybean. Genetic analysis were performed under major gene + polygene mixed inheritance model in the P1, P2, F1, and BC1F3 of the cross Essex×ZDD2315. The results showed that fat content and linolenic acid content of the cross were controlled by two major genes plus polygenes, with the major gene heritability of 16.23%, and 41.98%, respectively, and polygene heritability of 53.49%, and 24.17%, respectively. Three major genes and polygenes contributed to the inheritance of palmitic, linoleic and stearic acids contents, with the major gene heritability of 71.63%, 91.59%, and 91.51%, respectively, and polygene heritability of 14.78% in palmitic acid, but no polygenes detected in linoleic and stearic acids. The inheritance of oleic acid content was controlled by three major additive genes, with the heritability of 74.66%. Correlation analyses between fat and fatty acid composition content showed that negative correlations with significant level of 1% were found among fat, palmitic and linolenic acids(-0.272,-0.325); oleic,linoleic and linolenic acids(-0.833,-0.604); palmitic and oleic acids(-0.255);and between linoleic and stearic acids(-0.310). Positive correlation with significant level of 1% existed between oleic and linoleic acids(0.287). Negative correlation with significant level of 5% was found between palmitic and linoleic acids(-0.211). The inheritance of fat and fatty acid composition content in soybean involved with both major genes and polygenes. While for other fatty acids mainly due to major genes with their heritability of more than 70%, the major gene heritability of fat and linolenic acid contents were smaller. In the improvement of fat content, accumulating polygenes should be emphasized, while utilization of major genes is preferred for fatty acid improvement. There will be no serious contradictions in the improvement of both fat content and fat quality traits.Based on the genetic research above, QTL mapping for fat and fatty acid composition contents in soybean was carried out as following. The mapping population with 114 BC1F1 plants of the backcross (Essex×ZDD2315)×ZDD2315 was established and tested for their genetic variation , and then used to construct a genetic linkage map with 250 SSR markers plus one morphological marker, i, spanning 25 linkage groups (LG), each with 2 to 20 markers, at a total distance of 2963.5 cM, and average marker distance of about 11.8 cM. The methods of composite interval mapping (CIM) and multiple interval mapping (MIM) of software Win QTL Cartographer Version 2.5 were used for QTL mapping. With CIM method, 18 QTLs ( namely fat-1, fat-2, pal-1, pal-2, pal-3, st-1, st-2, st-3, ole-1, ole-2, ole-3, lin-1, lin-2, lin-3, lin-4, lio-1, lio-2, lio-3 ), conferring the contents of fat and fatty acid composition in soybean seed were mapped on nine LGs, i.e. B2, C1, D1b-1, D2, E, H-1, I, L and N-1, explaining 8.2%-39.3% of the total phenotypic variation, while with MIM method, nine QTLs were detected on six LGs, i.e. B2, C1, D1b-1, D2, H-1 and N-1, explaining 9.6%-34.5% of the total phenotypic variation. Of which seven QTLs, i.e. fat-1, pal-1, st-1, ole-1, lin-1, lin-4 and lio-2, were located on the same regions as that under CIM, the other two, i.e. ole-4 and lin-5, were close to those under CIM. The other nine QTLs detected with CIM, but not with MIM, need to be further verified. Six SSR markers, which co-segregated with or closely linked to fatty traits of soybean, were selected. The number of major QTLs with large effect conferring the contents of fat and fatty acids appeared not as many as expected, while the minor QTLs with small effect accounted for a certain amount of the variation. Therefore, both major and minor QTLs should be considered in the improvement of fat quantity and quality in soybean seeds.Investigating results of variations of soybean fatty traits from different eco-regions by principal component analysis method can be a reference to soybean fat quality breeding nation-widely. The results of inheritance mechanism of fat and fatty acid composition of soybeans, obtained by major gene + polygene mixed inheritance model, and by QTL mapping, respectively, are relatively in consistency; molecular markers screened in this study, closely-linked to or co-segregated with soybean fatty traits, can also be a reference to soybean fat quality breeding with marker assisted selection (MAS).But the results of this research are preliminary and tentative. For the number of fat quality genes and their exact positions are still to be known; the variation of fatty traits of soybeans needs to be verified because of lack of significant test. Therefore, further research work on these fields should be continued. |
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