Construction of a high-density genetic linkage map and identification of quantitative trait loci associated with clubroot resistance in radish ( Raphanus sativus L. )

Clubroot is a devastating disease caused by Plasmodiophora brassicae , leading to substantial yield loss of cruciferous plants, especially radish ( Raphanus sativus ) in China. Thus, there is a need to elucidate the mechanisms underlying the pathogenicity of P. brassicae and to breed clubroot-resistant radish cultivars. In the present study, we constructed a high-density linkage map of R. sativus by restriction-site-associated DNA sequencing (RAD-Seq) using an F 2 population derived from a cross between the clubroot-resistant and clubroot-susceptible inbred lines “BJJ” and “XNQ,” respectively. The genetic map spans 794.3 cM and has 1148 SNPs distributed across nine linkage groups corresponding to the nine chromosomes of R. sativus . The average distance between the adjacent markers is 0.7 cM. A set of five QTLs (viz., RsCr1 , RsCr2 , RsCr3 , RsCr4 , and RsCr5 ) associated with resistance to clubroot was detected on chromosomes 8 and 9. The limit of detection values of quantitative trait loci (QTLs) ranged from 5.23 to 7.65, accounting for 7.26–31.38% of the observed phenotypic variance. Synteny analysis showed that RsCr1 is homologous to the clubroot resistance gene Crr1 in Brassica rapa . This high-density genetic map of R. sativus provides valuable information for clubroot resistance gene selection and resistant variety breeding, while the QTL mapping results provide a reference dataset for effective gene exploration and marker-assisted breeding programs.