Key quantitative trait loci controlling bolting tolerance in sugar beet

For nonseed crops reliant on roots, leaves, and stems, breeding bolting-tolerant varieties is vital, and understanding the genetic mechanism aids effective selection. In sugar beet (Beta vulgaris), which accumulates sugar in roots, sequencing variations of BvBTC1, the master gene controlling annual and biennial life cycles, is associated with bolting tolerance, but the effects have not been demonstrated. We conducted quantitative trait loci (QTL) analysis on two generations (F2:3 and F5:6) from diverse bolting-tolerant crosses. Over 4 years, using phenotypic and mainly amplified fragment length polymorphism-based genotypic data, we identified two consistent QTLs: qB2 and qB6. These loci, detected regardless of the survey year or generation, were found to be crucial for enhancing sugar beet's bolting tolerance. qB2 on chromosome 2 exhibited the highest phenotypic variance (PVE; 41.9-66.6%) and was attributed to BvBTC1 based on mapping and gene function. On chromosome 6, qB6 (PVE 7.8-23.7%) was located near bolting-related genes, such as Bv_22330_orky and BvFL1, but the gene responsible for qB6 remains unclear owing to map information limitations. Overall, the key QTL qB2 and qB6 hold promise for advancing bolting tolerance in sugar beet, offering valuable insights for targeted breeding efforts.