GENETIC-MAPPING OF AGRONOMIC TRAITS USING RECOMBINANT INBRED LINES OFSOYBEAN

Many agronomic traits of interest to plant breeders are quantitative. Recombinant inbred (RD lines are particularly useful in genetic mappin g studies of quantitative traits. A recombinant inbred population was derived from the Glycine max (L.) Merr. parents 'Minsoy' and 'Noir 1'. This soybean population was used to investigate the genetic basis of several agronomic traits: days to flower (R1), days to maturity (R8), reproductive period (R8-R1), plant height, lodging score, height divid ed by lodging (the ability of tall plants to stand upright), seed prot ein content, seed oil content, seed size, yield, seed number, yield di vided by height (the yield from short plants), leaf width, leaf length , and leaf area. In this RI population, transgressive segregation was observed for all of these traits. As expected, height and lodging were correlated, as were height and maturity; height and maturity with yie ld; and leaf length and width with leaf area. Height divided by lodgin g and yield divided by height showed little correlation with other tra its, indicating that these traits measured new plant phenotypes. A gen etic map was constructed for this population, with restriction fragmen t length polymorphism markers, simple sequence repeat markers and clas sical markers. Approximately 2000 cM of linkage was defined. The data were used to identify quantitative trait loci (QTLs) by linking quanti tative phenotypes to qualitative genetic markers. For many traits, a f ew QTLs accounted for a large proportion of the variation observed. QT Ls for most of the traits were associated with three linkage groups, o ften with the same genetic locus within the linkage group. At the leve l of resolution of the genetic map for this population, it was not pos sible to determine whether these QTLs have pleiotrophic effects or are clusters of separate, tightly linked genes. The data suggest that sep aration of QTLs for different traits (such as maturity or lodging and yield) may be difficult, but that this RI population will be useful in resolving questions concerning marker assisted selection of quantitat ive traits.