Aquaculture Europe 2014

October 14-17, 2014

Donostia–San Sebastián, Spain

QTL ASSOCIATED TO RESISTANCE TO BACTERIAL COLD WATER DISEASE IN RAINBOW TROUT

E. Quillet1*, N. Dechamp1, C. Hervet1, F. Krieg1, C. Chantry-Darmon2, M. Boussaha1, A. Bérard3, V. Laurens4, T. Rochat5, E. Duchaud5, P. Boudinot5, J-F. Bernardet5, C. Michel5
 
1INRA, UMR 1313 GABI, F-78350 Jouy-en-Josas, France, 2LABOGENA, F-78350 Jouy-en-Josas, France, 3INRA, US 1279 EPGV (Etude du Polymorphisme des Génomes Végétaux), CEA/Institut de Génomique/Centre National de Génotypage, 4INSERM UMR 866, Université de Bourgogne, Institut Fédératif de Recherche Santé STIC, F-21000 Dijon, France, 2 rue Gaston Crémieux, F-91057, Evry Cedex, France, 5INRA, UR 892, F-78350 Jouy-en-Josas, France
E-mail : edwige.quillet@jouy.inra.fr

Introduction
Flavobacterium psychrophilum, the bacterial agent responsible of the Bacterial Cold Water disease (BCWD) is one of the most significant pathogen in salmonids worldwide. Selective breeding for resistance seems a promising method to control the disease. However, selection for disease traits is hampered by the difficulty to get related phenotypes, and the discovery of genetic markers associated to resistance is expected to substantially help at designing efficient selection schemes. A collection of rainbow trout gynogenetic clonal lines has been established at INRA. The lines were screened for resistance to several pathogens (Biacchesi et al., 2007; Quillet al., 2007; Verrier et al., 2013), including F. psychrophilum and exhibited a wide range of survival after infection with the bacterium, which makes them a relevant experimental resource to investigate the genetic bases of resistance. A first description of transcriptome response to infection was also performed in lines with opposite resistance (Langevin et al., 2012). In this study, we searched for resistance QTL in a doubled haploid F2 progeny from two clonal lines chosen for opposite resistance.
 
Material and methods
Two F0 homozygous individuals from a resistant (R) and a susceptible (S) gynogenetic clonal respectively were used as grand-parents of the QTL family. F1 females (S female x R male) were reproduced by gynogenesis to produce doubled haploid F2 progeny. For infection, bacterial suspension of the JIP02/86 F. psychrophilum isolate was produced according to standard procedures (Garcia et al., 2000). About 280 fish (6.3g mean body weight) were infected through intramuscular injection (4.2 105 cfu/fish) at INRA facilities (IERP, Jouy-en-Josas, France) and mortality was recorded daily during one month.
For the genome-scan, all fish (dead and survivors) were genotyped at 217 microsatellite and 101 SNP markers. QTL detection was performed with QTLMAP software (Filangi et al., 2010). The Cox model-based survival analysis for non-normal distribution and presence of censored data (Moreno et al., 2005) was used to analyze resistance phenotypes.
 
 
Results
QTL for survival were detected on 6 different chromosomes, three of them having a strong effect on survival (linkage group RT12, RT19 and RT31).  In order to get further insight into the possible defense mechanisms, the QTL positions were compared to those of several immune candidate genes that were mapped in the QTL family. Among the investigated genes, including interleukins (IL6, IL10), MH genes (MH1-A or UBA, MH1-B or UAA, MH1-C or MH-II and TAP1) and Toll-like receptors (TLR3, TLR22), there was suggestive evidence of a possible role only for TAP1, an antigen peptide transporter. The possible effect of the main QTL on bacterial load in the spleen is also being investigated.
 
Discussion and conclusion
The detection of QTL with significant effects on resistance to F. psychrophilum further confirmed the existence of a genetic basis of resistance to the bacterium in domestic populations of rainbow trout and paves the way towards the future discovery of relevant markers to be used in selective breeding for improved resistance.
 
References
Biacchesi, S., Le Berre, M., Le Guillou, S., Benmansour, A., Brémont, M., Quillet, E., Boudinot, P., 2007. J.Fish Dis, 30: 631-636.
Filangi, O., Moreno, C., Gilbert, H., et al., 2010. In Proc. 9th WCGALP: 1-6 August; Leipzig, 2010: n°787.
Garcia, C., Pozet, F. and Michel, C., 2000. Dis. Aquat. Org., 42:191-197.
Langevin, C., Blanco, M., Martin, S.A.M., et al., 2012. PLoS ONE 7(6) : e39126.
Moreno, C., Elsen, J-M., Le Roy, P. et al., 2005. Gen. Res. (Camb) 85 : 139-149.
Quillet, E., Dorson, M, Le Guillou, S. et al., 2007. Fish Shellfish Immunol. : 22,510-19.
Verrier, E.R., Ehanno, A., Biacchesi, S., et al., 2013. Fish Shellfish Immunol. 35 : 9-17.