Assessing selection potential for Pacific oyster (Crassostrea gigas) to a North American OsHV-1 µvar: Comparing two experimental assay methods

Authors: Thompson, Neil; AGNEW, VICTORIA - University Of Maryland; Calla, Bernarda; BURGE, COLLEEN - California Department Of Fish & Game

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/2024
Publication Date: 5/11/2024
Citation: Thompson, N., Agnew, V.M., Calla, B., Burge, C.A. 2024. Assessing selection potential for Pacific oyster (Crassostrea gigas) to a North American OsHV-1 µvar: Comparing two experimental assay methods. Aquaculture. Vol 590. https://doi.org/10.1016/j.aquaculture.2024.741076.
DOI: https://doi.org/10.1016/j.aquaculture.2024.741076

Interpretive Summary: A more virulent microvariant of a virus (OsHV-1) that has decimated Pacific oyster aquaculture on numerous continents has been identified in San Diego Bay California. This represents the first detection of an OsHV-1 microvariant in North America and poses a significant threat to the Pacific coast shellfish industry if the virus expands its range. Genetic selection programs have successfully bred for increased survival in Pacific oysters when challenged with the virus, yet no study has evaluated if breeding populations available to the USDA ARS harbor the necessary characteristics for a successful selection program against the novel microvariant. We challenged oysters with the San Diego microvariant in the laboratory and found that survival was highly heritable, the breeding population has suitable genetic variation for a selection program and that two methods for challenging oysters with this virus produced very similar results. Overall, given the standing genetic variation within the Pacific oyster population studied, it is a suitable group to use for embarking upon a genetic selection program to pro-actively develop higher survival against the OsHV-1 microvariant for the Pacific coast shellfish industry.

Technical Abstract: Ostreid Herpesvirus - 1 is a global threat to Pacific oyster aquaculture as catastrophic farm losses have occurred where OsHV-1 microvariants (µvars) become endemic. Genetic selection has proven effective for increasing survival to OsHV-1 exposure in multiple Pacific oyster breeding programs, but a novel µvar detected in San Diego Bay has the potential to severely impact commercial aquaculture along the North American Pacific coast as no OsHV-1 µvar selected population is available commercially. Using a Molluscan Broodstock Program population descending from imports originating in the Miyagi prefecture (Japan), we evaluated the potential for genetic selection to improve survival against the San Diego Bay OsHV-1 µvar using a laboratory trial. Two experimental methods were evaluated, a common garden method where all 15 full-sibling families were pooled, and a petri dish method, where each family was confounded within replicate. No striking differences were found between experimental methods, and both experiments displayed high heritability (0.69 and 0.64) of the tested trait, a broad range of estimated breeding values, and a moderate prediction accuracy for the survival trait. A significant genotype-by-environment interaction occurred, highlighting variability in laboratory-based disease challenges, but the two experiments yielded similar results with minor to moderate re-ranking of family survival. Overall, the Miyagi population of Pacific oysters curated by the Molluscan Broodstock Program is a promising population to use for artificial selection to increase survival against San Diego Bay OsHV-1 µvar in attempts to obviate farm losses if the virus expands its currently isolated range.