Development of chromosome segment substitution lines in soybean

Identification of a responsible gene for a target trait provides an important insight for molecular basis on it. Since genome sequence information has been collected from a wide range of soybeans, many kind of genetic resources and utilization of the increasing sequence information are required to identify genes underlying target traits. Mapping population called chromosome segment substituted lines (CSSLs) containing a few chromosomal region from donor genotype become a powerful tool for such quantitative trait loci (QTLs) analysis. We developed CSSLs in soybean derived from a cross between Japanese elite cultivar "Enrei" which is second leading variety in Japan and Chinese cultivar "Peking" which has many biotic stress resistance genes. Our backcross population of which “Enrei” was used as a recurrent parent consisted of 1043 lines and the linkage map of BC₃F₂ population was constructed using 231 SSR markers. Average ratios of chromosomal segments from “Peking” integrated into the each line were well coincided with the theoretical ones. QTL analysis for flowering time identified not only known flowering/maturity loci but also some novel QTLs. By using selected backcross lines, some QTLs were successfully dissected into a single genetic factor and the locations of flowering QTL identified in CSSLs was found to be valid. We selected 103 BC₃F₃ lines as candidate CSSLs based on the SSR genotypes. The association between integrated segment(s) and flowering time evaluated in each line indicated that some additional flowering QTLs with minor effects have not yet characterized. We discussed the usefulness of developed CSSLs.