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Association Mapping of QTLs of Breeding Target Traits and Dissection of Genotypic Constitution of Major Soybean Cultivars in China

Author: WuKeZuo
Tutor: GaiJunZuo；ZhaoTuanJie
School: Nanjing Agricultural College
Course: Crop Genetics and Breeding
Keywords: Major soybean cultivar Linkage disequilibrium Association analysis Elite allele Genotipic constitution
CLC: S565.1
Type: Master's thesis
Year: 2009
Downloads: 41
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Abstract


Total 1300 soybean cultivars have been released during 1923 to 2005 in China, which represent the most important types of core collection for breeding purpose. To reveal the genetic base of these cultivars may provide theoretical and applied significance for the future breeding. A representative sample with 188 major cultivars from Huang-Huai valleys and Southern China were established to conduct association mapping of QTLs of breeding target traits. Fifteen phenotypic traits (including yield, quality, morphological and agronomical traits) were investigated, and genotypic data of 197 simple sequence repeat (SSR) markers were obtained. After population structure and linkage disequilibrium degree were analyzed by STRUCTURE software, association mapping was conducted by the GLM model of TASSAL program and Zhang Jun’s procedure. The main results were as follows:1. Extensive LD phenomena of SSR loci pairs were observed in the released cultivar population. It showed that LD loci pairs could be detect effectively under higher significant level in certain population. Under P＜0.001,7.82% of the total loci pairs performed LD, and 7.39% of the loci pairs of syntenic markers had high LD degree. LD decay occurs at the shortest distance of 0.16 cM when D’<0.5, and the value decayed quickly along with the increasing of genetic distance.2. The released cultivar population was divided into seven subpopulations by using the STRUCTURE software. There were 270 loci associated with breeding target traits according to the association mapping of 197 SSR markers. Among these loci, six had larger effects with the value more than 0.2 of the explained proportion of total phenotypic variation. However, only 136 loci (times) with breeding target traits were detected in the population by 85 SSR markers in the previous study. With the increase of significance level of association mapping, such as P＜0.005, the "ghost" associated loci with lower explanation of total phenotypic variation would be discarded, while the loci with high explained portion of phenotypic variation would be identified and remained. 3. Under P＜0.005,100 SSR loci associated with 15 breeding target traits were found, and accumulated 241 loci (times) were detected for different environment conditions. Among them,69 loci (times) were consistently detected in two experiment years, and 59 loci (times) located in the positions (±5cM) where QTLs were mapped by family-based linkage mapping procedure previously. Some elite alleles and their typical carriers were identified for yield,100-seed weight, protein content, oil content, and maturity traits.4. The best alleles related to yield,100-seed weight, protein content and oil content had different distribution frequencies in five family pedigrees (Nannong 1138-2, Nannong 493-1,58-161, Qihuang 1 Hao, and Xudou 1 Hao). It indicated that there existed different genetic base and improvement potentials of target traits in these populations. Analyses for transition of elite alleles of yield in the five cultivar pedigrees showed that yield increased with the increasing of the number of elite yield allele. According to the yield genotypes, strategies to pyramiding the elite alleles were suggested for further soybean design breeding.

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CLC: > Agricultural Sciences > Crop > Economic crops > Oil crops > Soybean
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