Identification of Additional Quantitative Trait Loci (QTL) Responsible for Susceptibility to Infectious Pancreatic Necrosis Virus in Rainbow Trout

Previous typing of microsatellite markers in a BC1F1 backcross rainbow trout Oncorhynchus mykiss revealed two quantitative trait loci (QTL) with a significant impact on suscep- tibility to infectious pancreatic necrosis. In the present study, additional genetic markers were mapped using the same strain in order to increase QTL resolution. A total of 199 individuals were screened at 226 marker loci (106 microsatellites, 116 amplified fragment length polymorphism markers, classical major histocompatibility complex molecules (MHC class I, nonclassical MHC class I, MHC class II) and tyrosinase) and the QTL were determined by single-point and interval mappings. Seven QTL were distinguished in the linkage groups RT-11, 12, 17, 23, 26, 29 and 31, in addition to the two already known in RT-3 and 22. The major QTL were those in RT-3, 12 and 22; whereas the classical MHC class I locus Onmy-UBA and the MHC class II locus Onmy-DAB were not associated with any of the QTL, a nonclassical MHC class I region with Onmy-UCA, Onmy-UDA, and Onmy-UEA mapped to the major QTL on RT-3.