Construction Of Genetic Linkage Map And QTL Mapping Of Important Traits In Soybean [Glycine Max (L.) Merrill]

The construction of genetic linkage groups and the mapping of QTL for quality, resistance and agronomic traits are main components of plant genomics research.In this study,two-hundred and fourty-four F₂ plants derived from a soybean(Glycine max) cross between Lishuizhongzihuang(P₁) and Nannong 493-1(P₂) were genotyped using 136 pairs of polymorphism simple sequence repeats(SSR) molecular markers.The molecular marker dataset was used to construction soybean genetic linkage groups using Joinmap software (version 3.0).Some important traits,i.e.,oil and protein contents,100-seed weight,and the resistance of soybean to Bean pyralid(Lamprosema indicata Fabricius) in F₂ population, the resistance of soybean to soybean mosaic virus(SMV) with strain Sa in the F_2:3 population,and the number of branches,the number of main-stem nodes and plant height in the F₂ and F_2:3 populations,were measured.The observations for the quantitative traits mentioned above,along with the molecular marker data and the linkage groups,were used to map their corresponding quantitative trait loci(QTL) using composite interval mapping and multiple interval mapping in the software of Windows QTL Cartographer V2.5.The main results were as follows.1.Sixty-six SSR markers were assembled into twenty-one linkage groups,which correspond with soybean chromosomes with specific markers in soybean public genetic groups.The length of each linkage group ranged from 17.71 cM to 129.33 cM and the total length was 1091.34 cM,with an average marker spacing of 16.53 cM.The linkage group with the largest average marker spacing of 43.55 cM was the Dlb,and the one with the smallest average marker spacing of 13.86 cM the M.There were 20 large gaps each being longer than 20 cM.Note that C2,D1b,M,N,O and D2 linkage groups were divided into two parts and there were no markers on the B1,B2,C1,G and L linkage groups.As compared with the public genetic groups,the order of the markers here was almost same but the distances between adjacent markers in this paper were larger.This indicates that the linkage map needs to be improved.2.Under the situation of the critical value of 2.0,sixty-three QTL were mapped on fifteen linkage groups.Among these QTL,most were on A2,N,O,D1b,D2,M,and C2 linkage groups,fifty-five interacted QTL were detected,there were 20 QTL each with heritability more than 0.10 and seven QTL each with heritability more than 0.20,and there were eleven interacted QTL each with heritability more than 0.10 and three interacted QTL each with heritability more than 0.20.2.1 For the number of branches,nine QTL in the F₂ and six QTL in the F_2:3 were detected. Among these detected QTL,there were ten interacted QTL in the F₂ or F_2:3,which accounted for more than 50%phenotypic variation,and the common three QTL that the first one,qFZS-D2-2,was located between markers satt488 and sat 354 on the D2 linkage group,the second one,qFZS-F,near to marker BE806387 on the F linkage group,and the last one,qFZS-O-2,between markers satt592 and satt331 on the O linkage group.2.2 For the number of main-stem nodes,five QTL in the F₂ and six QTL in the F_2:3 were mapped.Among these QTL,there were three interacted QTL in the F₂ and five interacted QTL in the F_2:3,which accounted for more than 20%phenotypic variation,and the common two QTL that one,qZJJS-F,was near to the marker satt348 on F linkage group and the other,qZJJS-C2-2,close to the marker satt277 on C2 linkage group.2.3 In the mapping of QTL for the resistance of soybean to SMV with strain Sa,two response variables including average disease rank(ADR) and synthetic disease index(SDI) were adopted in the F_2:3.For each response variable,six QTL were identified.Among the twelve QTL,there were seven interacted QTL for the ADR,which accounted for 27.04% phenotypic variation,four interacted QTL for the SDI,which accounted for 76.23% phenotypic variation,and the common two QTL that one,qHYP-C2-1,were between markers satt422 and satt640,and the other,qHYP-N-1,between markers sat₂80 and satt683.2.4 For the resistance of soybean to Bean Pyralid in the F₂,four QTL were mapped on the A2,D1b-1,E and O linkage groups on which soybean insect resistance QTL were located.2.5 For protein content in the F₂,four QTL were detected on the C2,Dlb,I and J linkage groups.Among these QTL,two interacted QTL that accounted for 16.18%phenotypic variation were mapped.2.6 For 100-seed weight in the F₂,three QTL were detected on the D1a,E and F linkage groups.Among these QTL,there were three interacted QTL that accounted for 28.57% phenotypic variation.2.7 For oil content in the F₂,eight QTL were located mainly on the C2 and N linkage groups.Among these QTL,there were three QTL each being more than 10%heritability, and five interacted QTL that accounted for 15.73%phenotypic variation.2.8 For plant height,two QTL in the F2 and four QTL in the F_2:3 were detected.Among the six QTL,there were one interacted QTL in the F₂ that accounted for 14.89%,five interacted QTL in the F_2:3 that accounted for 47.47%phenotypic variation,and no common QTL. However,qZG-F and qZG-O-2 on the F and O linkage groups in this article were consistent with those of Mian et al.(1998) and Wu et al.(2001),respectively.3.To further confirm and make use of the above results in QTL mapping,three QTL with maximum heritabilities were selected and their corresponding genotypes of markers closely linked the three QTL were assorted so that the average value and standard deviation for quantitative traits for each genotypic component could be calculated.Based on the results from the resistance of soybean to Bean Pyralid,the number of nodes,the resistance of soybean to SMV and the number of branches,the marker genotypes with the minimum and maximum average values for the four traits were not consistent with those of female(or male) parent,and were a marker genotypic component between female and male parents. This further confirms that there is interaction between QTL.