Location: Cool and Cold Water Aquaculture Research
Title: Detection of quantitative trait loci (QTL) for resistance to bacterial cold water disease and spleen size in rainbow trout Authors
Submitted to: Aquaculture America Conference
Publication Type: Abstract Only
Publication Acceptance Date: December 1, 2011
Publication Date: February 28, 2011
Citation: Palti, Y., Vallejo, R.L., Welch, T.J., Evenhuis, J., Leeds, T.D., Liu, S., Rexroad III, C.E., Wiens, G.D. 2011. Detection of quantitative trait loci (QTL) for resistance to bacterial cold water disease and spleen size in rainbow trout. Aquaculture America Conference. 4. Technical Abstract: Bacterial cold water disease (BCWD) causes significant economic loss in salmonid aquaculture. We previously detected genetic variation in survival following challenge with Flavobacterium psychrophilum, the causative agent of BCWD in rainbow trout, and a family-based selection program to improve resistance was initiated at the National Center for Cool and Cold Water Aquaculture (NCCCWA) in 2005. We also previously reported a phenotypic correlation between spleen index (spleen weight normalized to body weight, SI) and family survival following F.psychrophilum challenge for two year classes (2005 and 2006) of rainbow trout. To understand the genetic architecture underlying variation in disease resistance, we made select crosses in 2007, 2008 and 2009 to assess disease resistance and correlated traits. In 2007, fifteen families were created from mating disease resistant (R) or susceptible (S) parents. In 2008, fifteen families were created from mating high SI (H) and low SI (L) parents. A positive phenotypic correlation between survival and SI was detected in multiple years, and spleen size was determined to be highly heritable. We initiated QTL mapping using family 20080132 from which 327 progeny were phenotyped for spleen size and 120 progeny phenotyped for 21 day post-challenge survival. Using selective genotyping, 196 fish were scanned with more than 300 microsatellite markers. Eighteen suggestive QTL (Pnominal<0.05) for spleen weight and spleen index were identified on 16 chromosomes, including three that were highly significant genome-wide (Pgenomewide<0.01) on chromosomes 5, 16 and 19. One significant QTL (Pgenomewide<0.01) for body weight was detected on chromosome 10. In 2009, ten backcross (BC) families and five F1 intercross (F2) families were produced to directly map QTL affecting resistance to BCWD. From each family, 200 fish were challenged in four replicates per family. Genome scanning of three families with over 300 markers spaced at <10cM intervals is currently under way. In summary, both survival and correlated traits have been used to investigate the genetic basis of BCWD resistance and candidate QTL will be utilized to enhance selective breeding efforts at the NCCCWA.