Mapping of QTLs detected in a Brassica napus DH population for resistance to Sclerotinia sclerotiorum in multiple environments

Sclerotinia stem rot, caused by the fungus Sclerotinia sclerotiorum, is one of the most devastating diseases of rapeseed (Brassica napus L.) in China. The two major factors limiting the development of disease resistance are (1) the absence of accessions with complete resistance and (2) the lack of a single method that can be widely applied to assess tolerance-even though accessions with differential tolerance to S. sclerotiorum have been identified in China. In the study reported here, we have used one doubled haploid (DH) population consisting of 72 lines, which was derived from the F(1) generation of a cross between a partially resistant line (DH821) and a susceptible line (DHBao604), to identify quantitative trait loci (QTLs) involved in the resistance to S. sclerotiorum. Three inoculation methods, namely, mycelial toothpick inoculation (MTI), mycelial plug inoculation (MPI), and infected petal inoculation (IPI), were used to assess resistance at the adult plant stage. A genetic linkage map with 20 linkage groups covering 1746.5 cM, with an average space of 6.93 cM, was constructed using a total of 252 molecular markers, including 91 simple sequence repeats, 72 randomly amplified polymorphic DNA, 86 sequence-related amplified polymorphisms, two restriction fragment length polymorphisms, and one expressed sequence tag. Composite interval mapping identified ten, one and ten QTLs using MTI, MPI and IPI methods, respectively, at a LOD > 2.5. One QTL was detected in linkage group N12 by MTI in 2004 and 2005 and by IPI in 2005. Another QTL was detected in linkage group N3 and N4 by MPI in 2006 and 2007. There was one common QTL detected by MTI in 2005 and by MPI in 2006. These results provide information on the genetic control of resistance to S. sclerotiorum in oilseed rape.