Quantitative trait loci in Two Soybean Recombinant Inbred Line Populations Segregating for Yield and Disease Resistance.

Molecular makers linked to quantitative trait loci (QTL) can assist soybean [Glycine max (L.) Merr.] breeders to combine traits of low heritability, such as yield, with disease resistance. The objective of this study was to identify markers linked to yield QTL in two recombinant inbred line (RIL) populations ['Essex' x 'Forrest' (ExF; n = 100) and 'Flyer' x 'Hartwig' (FxH; n = 94)] that also segregate for soybean cyst nematode (SCN) resistance genes (rhg1 and Rhg4). Each population was yield tested in four environments between 1996 and 1999. The resistant parents produced lower yields. Heritability of yield across four environments was 47% for ExF and 57% for FxH. Yield was normally distributed in both populations. High yielding, SCN resistant transgressive segregants were not observed. In the ExF RIL population, 134 microsatellite markers were compared against yield by ANOVA and MAPMAKER QTL. Regions associated with yield were identified by SATT294 on linkage group (LG.) C1 (P = 0.006, R(2) = 10%), SATT440 on LG. I (P = 0.007, R(2) = 10%), and SATT337 on LG. K (P = 0.004, R(2) = 10%). Essex provided the beneficial allele at SATT337. Mean yields among FxH RILs were compared against 33 microsatellite markers from LG. K. In addition 136 markers from randomly selected LGs were compared with extreme phenotypes by bulk segregant analysis. Two regions on LG. K (20 cM apart) associated with yield were identified by SATT326 (P = 0.0004, R(2) = 15%) and SATT539 (P = 0.0008, R(2) = 14%). Flyer provided both beneficial alleles. Both populations revealed a yield QTL in the interval (5 cM) between SATT337 and SATT326. These populations may share a common allele for yield in this region, given that about 40% of Flyer genome derived from Essex.