Title : Mapping and validation of QTLs for cabbage black rot resistance
Abstract:
Black root (BR), a main serious disease of cabbage (Brassica oleracea L.), is caused by the bacterial Xanthomonas campestris pv. campestris. To identify QTLs for resistance to BR, we constructed a cabbage genetic map using 303 SSR markers with an average interval of 2.77cM based on RILs developed from R4-P1 (resistant) and R2-P2 (susceptible). Race1 of Xcc were used to spray inoculation the RILs seedings, the disease indexs (DIs) were collected two weeks after inoculation based on infected leaf area. Using IciMapping 3.2, 11 QTLs were detected, only one major stable QTL on chromosome 7 was associated with resistance in both two mapping population. The QTL was located in a 2.91Mb interval based on the R2-P2 reference genome sequence defined by simple sequence repeat (SSR) markers M35 and M25. Nine annotated resistance genes in this region were collected, then these genes were sequence aligned and the expression level in different time stages after inoculation were analysed between two parents. According to the sequence differences and expression levels of these candidate genes, we concluded that Bo7g111290 is more likely the BR resistance gene to Race1 of Xcc in R4-P1. Our results provide a basis for further QTL fine mapping and candidate genes cloning, will promote pyramiding Xcc resistance genes in cabbage. Key Words: Brassica oleracea L., black root resistance, Xanthomonas campestris pv. Campestris, QTL, chromosomal segment substitution line.
