QTL Mapping and Candidate Gene Identification of Swollen Root Formation in Turnip.

The swollen root is an important agronomic trait and is a determinant of yield for turnips, which are cultivated as both vegetables and fodder. However, the genetic mechanism of swollen root formation is poorly understood. In this study, we analyzed the F and BCP populations derived from a cross between "10601" (European turnip with swollen root, ssp. , AA, 2n = 2× = 20) and "10603" (Chinese cabbage with normal root, ssp. , AA, 2n = 2× = 20), and suggested that the swollen root is a quantitative trait. Two major quantitative trait loci (QTLs), (Fleshy root 1.1) and (Fleshy root 7.1), were identified by QTL-seq analysis and further confirmed by QTL mapping in F and BCP populations. The QTL with a likelihood of odd (LOD) of 7.01 explained 17.2% of the total phenotypic variations for root diameter and the QTL explained 23.0% (LOD = 9.38) and 31.0% (LOD = 13.27) of the total phenotypic variations in root diameter and root weight, respectively. After a recombinant screening, the major QTL was further narrowed down to a 220 kb region containing 47 putative genes. A candidate gene, , which is a homolog of that plays an essential role in cell adhesion and disorganized tumor-like formation in , was identified in this region. In addition, expression and parental allele analysis supported that was a possible candidate gene of QTL for swollen root formation in turnip. Our research may provide new insight into the molecular mechanism of swollen root formation in root crops.