Quantitative Trait Locus (QTL) Mapping of Sugar Yield-Related Traits in Sugar Beet (Beta vulgaris L.)

Quantitative trait locus (QTL) mapping of sugar yield-related traits can promote the discovery of new sugar yield-related genes. Subsequently, marker-assisted selection (MAS) can be used to breed new high-yield sugar beet varieties. In this study, we observed the F-1 population (219 individuals) from a cross of 3a (high-yield, low-sugar, diploid, monogerm, sterile line) and 3b (low-yield, high-sugar, diploid, polyembryonic, pollinated line) parents located in Gaomi City, Shandong Province, China. A total of four traits (root length, root perimeter, root weight, and sugar content) exhibited a normal distribution. Based on a high-density genetic map, including 3287 specific-length amplified fragment markers and nine linkage groups (LGs) with an overall genetic distance of 1554.64cM, a total of 32 QTLs were identified for the four aforementioned traits. The QTLs were distributed on LG2, LG3, LG5, LG7, and LG9. The root length was mapped to six regions of LG2. The phenotypic variance explained (PVE) ranged from 6.30% to 8.03%. The root perimeter was mapped to five regions of LG5 and 12 regions of LG7. The largest PVE was on LG5 (7.23%). The root weight was mapped to two regions of LG3 and three regions of LG7. The four sugar content-related QTLs located on LG5 and LG9 had a threshold logarithm of odds (LOD) value of 4.35 and a max PVE of 10.13%, indicating a potentially important QTL for future gene cloning. Using trait-based QTL mapping and chromosomal marker distribution data, we identified 3690 candidate genes including 191 root length, 918 root perimeter, 409 root weight, and 2172 sugar content genes. Our results provide valuable information for additional research in fine mapping, gene functional analysis, pyramid breeding, and MAS.