QTL architecture of reproductive fitness characters in Brassica rapa

BACKGROUND: Reproductive output is critical to both agronomists seeking to increase seed yield and to evolutionary biologists interested in understanding natural selection. We examine the genetic architecture of diverse reproductive fitness traits in recombinant inbred lines (RILs) developed from a crop (seed oil) × wild-like (rapid cycling) genotype of Brassica rapa in field and greenhouse environments. RESULTS: Several fitness traits showed strong correlations and QTL-colocalization across environments (days to bolting, fruit length and seed color). Total fruit number was uncorrelated across environments and most QTL affecting this trait were correspondingly environment-specific. Most fitness components were positively correlated, consistent with life-history theory that genotypic variation in resource acquisition masks tradeoffs. Finally, we detected evidence of transgenerational pleiotropy, that is, maternal days to bolting was negatively correlated with days to offspring germination. A QTL for this transgenerational correlation was mapped to a genomic region harboring one copy of FLOWERING LOCUS C, a genetic locus known to affect both days to flowering as well as germination phenotypes. CONCLUSIONS: This study characterizes the genetic structure of important fitness/yield traits within and between generations in B. rapa. Several identified QTL are suitable candidates for fine-mapping for the improvement of yield in crop Brassicas. Specifically, brFLC1, warrants further investigation as a potential regulator of phenology between generations.