Association between DNA polymorphisms tightly linked to MHC class II genesand IHN virus resistance in backcrosses of rainbow and cutthroat trout

Infectious hematopoietic necrosis (IHN) is a rhabdoviral disease of salmoni d species. Single strand conformation polymorphism (SSCP) was used to ident ify association between DNA polymorphism of the major histocompatibility co mplex (MHC) class II beta-chain intron and IHN virus (IHNV) resistance in b ackcrosses of rainbow trout (Oncorhynchus mykiss) and cutthroat trout (O, c larki). Association was significant (P = 0.024) in four half-sib families f rom one sire (number 2), but not among half-sibs from another sire (number 1), DNA sequencing analysis revealed that the polymorphism originating from sire 1 is the result of a single base substitution. Sire 2 polymorphism wa s caused by three different base substitutions. The source of the susceptib le allele appears to be from cutthroat trout and not from the rainbow trout population used to produce the hybrids, The results suggest that MHC polym orphism can contribute to linkage and association studies of immunity to in fectious diseases in rainbow trout. (C) 2001 Elsevier Science B.V. All righ ts reserved.