565. Conserved QTL and chromosomal inversions affect resistance to columnaris disease in two rainbow trout populations

Abstract

We present a comparative genetic analysis of the loci underlying genetic variation in mortality caused by warm water columnaris disease (CD) in farmed rainbow trout (Oncorhynchus mykiss) populations. We provide evidence for the conservation of major QTLs, and the putative role played by chromosomal rearrangements in determining resistance to CD. We genotyped 3,962 individuals from two populations experiencing a natural Flavobacterium columnaris outbreak. Association analyses identified a major QTL in both populations on chromosome Omy3 and a secondary on Omy5. The QTL on Omy5 was within a naturally occurring major inversion, for which we were able to determine that the ancestral haplotype was associated with lower mortality. Genetic correlation between mortality in the two populations was estimated at 0.64, implying that the populations share much of the same genetic architecture for mortality. Our QTL validation suggests that QTLs could be used in marker-assisted selection, or specifically modelled in genomic evaluation to improve resistance by selective breeding.