Abstract: 【Objective】 Roots provide nutrition and affect crop yields. Root traits are believed to be complex and controlled by many genes, which show stability in different environments and present higher heritability. Study of such traits by QTL mapping of roots at seedling stage is needed for effective heredity breeding in soybean. The map spanned 2 047.6 cM across 27 linkage groups that contained 232 markers. 【Method】 With the methods of segregation analysis on the major-polygene mixed inheritance and composite interval mapping, a soybean SSR genetic linkage map constructed by a total of 447 recombinant inbred lines (RILs) derived from a cross between Jindou 23 (cultivar, female parent) and Huibuzhiheidou (semi-wild; male parent, ZDD2315) were used to analyze and identify the QTLs of root traits during seedling stage in soybean. Thirty seeds from each of the RILs and their parents were covered with pasteurized paper, and cultivated in clean water at 20-28℃ on 27 May, 2013, and the experiment was finished on 28 June, 2013. A complete random design with three replications was used. Root traits were measured on 8 June and 8 July at V2 stage.【Result】This grouping was supported by significant positive correlations among MRL, LRN, RW, RV and SW. There were highly significant positive correlations between HL and HW, and HL and SW. Root traits showed mutual influence and restriction, laying a foundation for selection of phenotypic traits. The inheritance analysis showed that the length of main root was controlled by three pairs of equivalent major genes; the number of lateral roots was controlled by two pairs of major genes; the weight and volume of root were controlled by four pairs of major genes; the length of hypocotyl was controlled by four pairs of additive major genes; the weight of hypocotyl was controlled by four pairs additive-additive × additive epistatic major genes. The polygene effect wasn’t found in all above root traits. The weights of leaf and stems were controlled by additive genes, but didn’t find major gene effects. Twenty-four QTLs associated with length of main root, number of lateral root, volume of root, weight of leaf and stems, length of hypocotyl and weight of hypocotyl were mapped on A1, A2, B1, B2, C2, D1b, F_1, G, H_1, H_2, I, K_2, L, M, N and O linkage groups respectively. Five QTLs for MRL were identified on linkage groups B1, L, N and O, respectively. The variation accounted for by each of these five QTLs ranged from 7.05% to 13.18%. Four QTLs for LRN were identified on linkage groups A1, D1b, I and L. The phenotype variation accounted for by each of these four QTLs ranged from 8.21% to 16.43%. Three QTLs for RW were identified on linkage groups F_1, G and N, respectively; the phenotype variation accounted for by each of these three QTLs ranged from 7.55% to 10.85%. Three QTLs for RV were identified on linkage groups K_2 and M based on the data from 27 May. The phenotype variation accounted for by each of these three QTLs ranged from 8.44% to 12.39%, but the main QTL was not detected in the experiment on 28 June. Five QTLs for SW were identified on linkage groups A1, A2 and N. They accounted for phenotype variation ranging from 11.43% to 38.91%. qSW1-a2-1, qSW2-a2-1 and qSW2-a2-1 were all located on chromosome A2. Based on the data for HL on 27 May, the QTL was located in linkage group H_1. It explained 7.86% of the phenotype variation, but the main QTL was not found on 28 June. Three QTLs for HW were identified on linkage groups B2, C2 and H_2. They accounted for phenotype variation ranging from 7.70% to 12.48%.【Conclusion】The inheritance control of root traits is very complicated. Root traits have complex genetic mechanisms at the seedling stage. This study has provided a foundation for further research on root genetic regulation and molecular breeding with emphasis on correlations among root traits to ensure robust root growth and well-developed root systems.

Key words: soybean , root traits , seedling stage , genetic , QTL