Co-location of QTL for Sclerotinia stem rot resistance and flowering time in Brassica napus

Sclerotinia stem rot (SSR) caused by Sclerotinia sclerotiorum (Lib.) de Bary is one of the most devastating diseases of Brassica napus worldwide. Both SSR resistance and flowering time (FT) adaptation are major breeding goals in B. napus. However, early maturing rapeseed varieties, which are important for rice-rapeseed rotation in China, are often highly susceptible to SSR. Here, we found that SSR resistance was significantly negatively correlated with FT in a natural population containing 521 rapeseed inbred lines and a double haploid (DH) population with 150 individual lines, both of which had great variation in FT. Four chromosomal regions on A2, A6, C2, and C8 affecting both SSR resistance and FT were identified using quantitative trait loci (QTL) mapping after constructing a high-density genetic map based on single nucleotide polymorphism markers in the DH population. Furthermore, we aligned QTL for the two traits identified in the present and previous studies to the B. napus reference genome, and identified four colocalized QTL hotspots of SSR resistance and FT on A2 (0-7.7 Mb), A3 (0.8-7.5 Mb), C2 (0-15.2 Mb), and C6 (20.2-36.6 Mb). Our results revealed a genetic link between SSR resistance and FT in B. napus, which should facilitate the development of effective strategies in both early maturing and SSR resistance breeding and in map-based cloning of SSR resistance QTL. (c) 2019 Crop Science Society of China and Institute of Crop Science, CAAS. Production and hosting by Elsevier B.V.