First evaluation of resistance to both California and French OsHV-1 variants in Pacific oysters

Authors: DIVILOV, KONSTANTIN - Oregon State University; SCHOOLFIELD, BLAINE - Oregon State University; MORGA, BENJAMIN - French Research Institute For The Expolotation Of The Sea (IFREMER); DEGREMONT, LIONEL - French Research Institute For The Expolotation Of The Sea (IFREMER); BURGE, COLLEEN - University Of Maryland; CORTEZ, DANIEL - Hog Island Oyster Co; FRIEDMAN, CAROLYN - University Of Washington; FLEENER, G - Hog Island Oyster Co; Dumbauld, Brett; LANGDON, CHRIS - Oregon State University

Submitted to: BMC Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/21/2019
Publication Date: 12/12/2019
Citation: Divilov, K., Schoolfield, B., Morga, B., Degremont, L., Burge, C.A., Cortez, D.M., Friedman, C.S., Fleener, G., Dumbauld, B.R., Langdon, C. 2019. First evaluation of resistance to both California and French OsHV-1 variants in Pacific oysters. BMC Genetics. 20:96. https://doi.org/10.1186/s12863-019-0791-3.
DOI: https://doi.org/10.1186/s12863-019-0791-3

Interpretive Summary: Recent outbreaks of an oyster herpes virus, known as OsHV-1, have caused mass mortalities and economic losses of Pacific oysters around the world. One of the most promising methods to safeguard the U.S. West Coast oyster industry, which is mostly dependent on Pacific oysters, is to breed oysters that are resistant to the virus. To identify resistant oysters, we exposed different oyster families from the Molluscan Broodstock Program, a West Coast Pacific oyster breeding program, to an American strain of the virus in the field and a European strain of the virus in a quarantined laboratory. The oyster families tested exhibited a spectrum of resistance levels, and the resistance to both strains of the virus was found to be under genetic, rather than environmental, control. Resistance levels of oysters between the two viral strains were not correlated which suggests that the virus interacts with oysters in a complex manner. Therefore, it is possible to selectively breed resistant US West Coast oysters, but more controlled experiments are necessary to unravel the complexities of virus-oyster interactions.

Technical Abstract: The ostreid herpesvirus-1 (OsHV-1) in Tomales Bay, California, USA and the OsHV-1 microvariant (µvar) in major oyster-growing regions outside of the United States cause very high mortalities of Pacific oysters. There are currently no known Pacific oysters in the United States that are resistant to OsHV-1. As part of an effort to begin genetic selection for resistance to OsHV-1, 71 families from the Molluscan Broodstock Program, a US West Coast Pacific oyster breeding program, were screened for survival to OsHV-1 in Tomales Bay. They were also tested in a quarantine laboratory in France where they were exposed to OsHV-1 µvar using a plate assay, with survival recorded from three to seven days post-infection. Significant heritabilities for survival were found for all time points in the plate assay and in the survival phenotype from a single mortality count in Tomales Bay. Genetic correlations among survival phenotypes across the two experiments were non-significant with the exception of a weak significant correlation between the survival at days three and seven in the plate assay and in the Tomales Bay field trial. It should be possible to breed Pacific oysters for increased survival to the Tomales Bay and µvar strains of OsHV-1 using families from the Molluscan Broodstock Program. The lack of a high correlation in survival between strains will require selection pressure for survival to each strain to make simultaneous genetic progress.