Inheritance And QTL Mapping Of Main Quality Traits Of Vegetable Soybean

Vegetable soybean (Glycine max (L.) Merrill), named Maodou in china, is not only the special variety in soybean but also a very important legume vegetable. It's fresh, tasty and rich in nutrition so that it becomes very popular with people in China and Southeastern Asian countries. In our county its capacity to earn foreign exchange through exports is very promising. At present, the requirements of vegetable soybean on the international markets are increasing gradually, but our country's research on vegetable soybean, compared with that from Japan and Taiwan province of China, isn't enough. Especially its edible quality is short of further research in genetics and breeding. The goal of this research was to understand genetic mechanisms that control seed quality related to the nutrition and commerce of vegetable soybean. Toward this end, We have undertaken an analysis of the accumulation law of development, genetic mechanisms and gene mapping on soluble sugar, starch, protein, fat, pod form, seed weight and shelling percentage. Some molecular markers tightly linked to the aimed target traits are obtained and thus would be helpful on quality improving of vegetable soybean via molecular marker-assisted selection(MAS). This has important theoretical and practical significance on enhancing international market competitiveness of vegetable soybean in our country. The main experimental results are as follows:First, three vegetable soybean cultivars, NAU95C-7, NAU95C-15 and NAU99-10, were used to study the developmental process of pod and seed qualities. The results showed as follows: The changes of pod form, such as length, width and thickness, with the days after flowering were well fitted with 'S' curve; the accumulations of 100-seed fresh weight and soluble sugar content with the days after flowering were well fitted with cubic equation; the suitable pod-picking period was suggested as during to medium-term of R₆ on the basis of yield and quality.Second, with the major gene plus polygene model of quantitative traits, a joint analysis of multi-generations from the two crosses NAU95C-7×NAU95C-15 and HuaiyuandaqingdouxJingxianxilihuang was carried out to investigate the inheritance of the soluble sugar, starch content, protein and fatty content. The results showed that the inheritance of four traits fitted two major genes plus polygene model. Heritability values of the major genes of F₂ population were estimated as 40.4%～85.8%, 77.4%～85.4%, 78.2 % and 71.9%, respectively, while the heritability values of those polygene were lower. In the improvement of vegetable soybean quality, accumulating polygenes should be emphasized, while utilization of major genes is preferred.Finally, based on the genetic research above, QTL mapping for soluble sugar content, starch content, shelling percentage and 100-seed fresh weight in vegetable soybean was carried out as following. The mapping population with 154 RIL plants of the cross BOGAO×NG94-156 was established and tested for their genetic variation, and then used to construct a genetic linkage map with 268 markers, spanning 24 linkage groups, at a total distance of 2854.9cM, and average marker distance of about 10.65 cM. The methods of composite interval mapping(CIM) of software Win QTL Cartographer Version 2.5 were used for QTL Mapping. With CIM method, twenty QTLs were mapped on 11 linkage groups: D1a, E, N, J, G, Cl-1, H-1, M-2, A1, A2, and I, explaining 6.65 %～15.57% of the total phenotypic variation. While with QTLmapper 1.6 software, 9 QTLs, located on the same regions or closely to those as that under CIM, were mapped on 8 linkage groups, i.e. Dla, E, N, J, G, M-2, A1 and A2, explaining 4.85%～12.93% of the total phenotypic variation. The other 11 QTLs detected alone with CIM, need to be further verified. Eleven SSR markers(Sat₁60, Satt234, Satt263, Sattl38, Satt285, Sattl38, Satt250, Satt684, Sat₃78, Sattl62 and Satt728), which co-segregated with or closely linked to quality traits of vegetable soybean, were selected. The number of major QTLs with large effect conferring the contents of quality traits 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 quantity and quality in vegetable soybeanThe results of inheritance mechanism of quantity of vegetable soybean, obtained by major gene and polygene mixed inheritance model and by QTL mapping, are relatively in consistency; molecular markers screened in this study, closely-linked to or co-segregated with vegetable soybean quality traits, can also be a reference to vegetable soybean quality breeding with molecular marker-assisted selection (MAS). For the number of quality genes and their exact positions still was unknown. The results of this research are preliminary and tentative. and should be studied in the successive research work.