QTL Mapping For Protein Content In Soybean By Using Backcross Introgression Lines

Soybean is animportant oil and food crop, comprising of about40%protein and20%oil in seeds.It contains the highest percentage of protein among legume crops, with well balanced amino acids,being an indispensable part of the diet of Asian residents. While increasing yield, improving the proteincontent of soybean seed has been a vital objective in soybean breeding program both at home andabroad.100BC₂F₃families were developed in2011by backcrossing using cultivar Zhonghuang13（containing46.58%protein）, as the recurrent parent, and Dongshan69（containing44.52%protein） asthe donor parent. Then BC₂F₄families were established by self-cross of BC₂F₃families in2012. Withthe pleomorphic SSR primers between parents, BC₂F₃families were genotyped by PCR amplification,Genetic structure was analyzed in the method of Chi-square test,and the effect of distorted markers wasdiscussed. By using SSR genotyped data, a linkage map was constructed by the QTL IciMapping V3.1*map, combining phenotype character, QTLs related to protein content in theZhonghuang13×Dongshan69BC₂F₃, BC₂F₄families were detected by one-way ANOVA and the ICIM,and the result was compared with that of previous studies, Zhonghuang13×Zhonghuang20BC2F2families were used to validate the major QTL detected in both environments. In the selectedintrogressing lines and random families of Zhonghuang13×Dongshan69BC₂F₃generation, QTLs werescreened by one-way ANOVA and Chi-square test based on the effect of genetic hitch-hiking, anddetection efficiency of different lines was compared, the main results were as follows:1. Analysis of genotype distribution and distorted segregation of markers in theZhonghuang13×Dongshan69BC₂F₃primitive populationSignificant distorted segregation was found through comparing populations of positive selection,negative selection, two-direction selection and random population with theoretical segregation ratio,. Inthe BC₂F₃random population,43（31.62%） out of136effective markers showed significant distortedsegregation （P≤0.01）. These markers are distributed in all linkage groups except B1, D2and L, of which15loci tended to deviate to Zhonghuang13. Three markers （6.98%） deviated to the donor parentDongshan69;12（27.91%） to heterozygotes;13（30.23%） to donor parents and hybrids at the same time.2. Identifying QTLs related to protein content in Zhonghuang13×Dongshan69BC₂F₃andBC₂F₄families（1） Detection of QTLs for protein content in Zhonghuang13×Dongshan69BC₂F₃andBC₂F₄families25loci were detected in the BC₂F₃families,16loci in the BC₂F₄families by one way-ANOVA;10loci were common in the two generations, and variation explained by the loci was almost more than10%.3intervals were identified in the BC₂F₃families,6in the BC₂F₄families by ICIMapping,2marker intervals were common and loci closely related to marker Satt155and Satt042on linkage groupA1, Satt296on linkage group D1b, and Satt206on linkage group F were common identified by bothANOVA and ICIMapping. With the result of different methods, we can conclude that considerable loci or marker intervals were identical in the BC₂F₃and BC₂F₄families.（2） Analysis of distorted loci detected by one way-ANOVA and ICIM7markers （17.07%） of41showed phenomenon of distortion （SD） when identified by one wayANOVA, and the variation was low （less than10%）;3marker intervals were distorted, occupying33.33%of all the9marker intervals identified by ICIMapping, and the phenotypic variance was almostgreater than10%, this indicated that SD may help ICIMpping detect major QTLs.3. Comparing the efficiency of detecting QTLs related to protein content by BC₂F₃selectedintrogression lines33QTLs were detected in all the four populations, Sat₁28, Satt703and Satt042was commonlyidentified in R60population, LOW20population and BS population, Satt703and Satt042were commonin R60population and BS population when all four BC₂F₃populations were analised by one-wayANOVA. It found that BS population was more effective than both LOW20population and TOP20population.When applying Chi-square test, number of QTLs detected in R60population, BS population,TOP20population and LOW20population were9,27,8and15, respectively as the theoreticalMendelian separation was used; While4,3and0QTLs detected in BS population, LOW20populationand TOP20population were identical with result of R60population identified by one way ANOVA.1,3and0QTLs identified in BS population, TOP20population and LOW20population were common tothe result of R60population analised by one way ANOVA It indicated that when theoretical.segregationratio was altered by theoretical genotyped segregation ration of random population,the efficiency ofQTL detection would be improved, the BS population performed better than TOP20population andLOW20population.