Construction Of Soybean Genetic Map And QTL Analysis Of Some Agronomic Traits

Genetic linkage maps serve the plant geneticist in a number of ways, from marker assisted selection in plant improvement to map-based cloning in molecular genetic research. Soybean, a widely studied and economically important species, is derived from ancient tetraploid and strictly self-pollinated. Its genome contains a large amount of duplication areas and repetitive sequences. The homology within the species is very high. For these reasons the research of genetic mapping in soybean is dropped behind the other crops. SSR markers play a critical role in integrating maps from different populations. One of the most important attempts in soybean genome research is to construct populations with large contents and facilities to locate special important agronomic traits.Jindou23 is a releasing cultivar in Shanxi province. It has properties of high yield, well resistance to drought and soybean mosaic virus (S2 strains and at least three of the other strains). But it is sensitive to soybean cyst nematode. Huibuzhi, a local germplasm of Shanxi province with black seed coat, is high resistant to soybean cyst nematode and sensitive to soybean mosaic virus. A cross of Jindou23 x Huibuzhi is made, then selfed for 8 generation by single seed descent method to construct RIL populations. SSR markers are used in evaluating the population. PCR markers-based genetic maps of this population were constructed and QTL tagging of some agronomic traits is also pursuing. Results are as follows:The 8th generation of RI population is constructed contained 487 lines. This population is the largest RIL population in current soybean research. And it is also the 3rd RIL population for genetic mapping and QTL tagging in our country.355 pairs of SSR primers, which cover almost the whole soybean genome, are used to evaluate randomly sampled population that contains 118 lines of this population. Evaluation shows that almost all of SSR loci and lines are purified. The content of Jindou23 & Huibuzhi is about 0.49 & 0.51, respectively, contributed to the sampled 118 lines population. The distribution of genotypic composition of the population fits normal well. Genetic distances of each pair of lines are calculated by Nei's method. The results of cluster by method UPGMA show that the population has less over presentation. In a word, the population is suit to genetic mapping and otter genetic research for its well-dispersed genetic structure.A genetic map based on PCR markers is constructed with this population. It spreads over 32 linkage groups and contains 117 markers including 104 SSR markers, 8 ISSR markers and 5 AFLP markers. The length of the map is 824.5 cM and the average of markers is 7.0 cM. It is easy to compare this map to soybean composite genetic map for most markers in this map are SSRs and it fits the composite genetic map well both in the sequences and the distances of markers. The trait of soybean black seed color is located onlinkage group A2 and 5.3 cM away from Sattl87.QTL tagging and analysis of soybean seed weight trait by method of composite interval mappling is pursued with our constructed map. 2 QTL are detected. One is located in Sattl67-Satt387 interval on LG g!8(K) and is 0.3 cM away from Sattl67. It can explain 13.7% of total variance. The other is located in Sat₀22-Satt256 interval on LG g28(D2). It is 0.02 cM to Satt₀22. Both are reductive effect and may from Huibuzhi.The same processes were done to detect QTLs of SMV resistance and of SCN resistance. One QTL of SMV resistance is detected and located in Sattl81-Sattl42 interval on LG g23(H), 2.02 cM away from SattlSl. It is addictive effect from Jindou23 and can explain 11.73% of total variance. One QTL of SCN resistance is located in Satt345-Satt479 interval on LG g22(O), 6.01 cM away from Satt345. It's reductive effect and may from Jindou23 and can explain 11.73% of total variance.