Fine Mapping and Identification of the Downy Mildew Resistance Gene BoDMR2 in Cabbage (Brassica oleracea L. var. capitata)

Background Cabbage (Brassica oleracea L. var. capitata ) is a crucial Brassica oleracea crop and is widely cultivated worldwide. In recent years, outbreaks of downy mildew caused by Hyaloperonospora parasitica have led to significant field losses in cabbage production. Thus far, there have been few reports on genes related to resistance to downy mildew in cabbage. Results In this study, sister lines exhibiting significant differences in disease resistance and susceptibility were identified. Using bulked segregant analysis followed by sequencing (BSA-seq) and linkage analysis, we precisely mapped the adult-stage cabbage resistance gene BoDMR2 to an ~ 300 kb interval on chromosome 7. Among the candidate genes, several single nucleotide polymorphisms (SNPs) and a 3-bp insertion were discovered in the conserved domain of Bo7g117810 in susceptible materials. Furthermore, quantitative real-time polymerase chain reaction (qRT‒PCR) analysis revealed that the expression level of the Bo7g117810 gene in resistant specimens was 2.5-fold greater than that in susceptible specimens. An insertion‒deletion (InDel) marker was subsequently designed based on the identified insertion in susceptible materials, facilitating the identification and selection of downy mildew-resistant cabbage cultivars. Conclusions This study identified BoDMR2 as a potential candidate gene associated with adult downy mildew resistance in cabbage, primarily based on differences observed in its gene sequence and expression levels. Additionally, an InDel marker was developed utilizing its mutation, thus offering valuable resources for cabbage resistance breeding