Effect of ploidy on the mortality ofCrassostrea gigasspat caused by OsHV-1 in France using unselected and selected OsHV-1 resistant oysters

Abstract

The effect of ploidy on the mortality of Crassostrea gigas spat caused by the ostreid herpesvirus (OsHV‐1) genotype μVar was investigated at five sites along the Atlantic coast in France in 2011. Sibling diploids and triploids were produced using either unselected or selected OsHV‐1‐resistant oysters. No significant interactions were found between the factors of environment, genotype and ploidy at the endpoint dates. The mean mortality rates at the sites were 62% and 59% for diploids and triploids, respectively, and the two rates were not significantly different. The mean mortality rates were 33% and 32% for sibling diploids and triploids, respectively, when OsHV‐1‐resistant parents were used and 91% and 85%, respectively, when unselected parents were used. The results were confirmed through other broodstocks tested in 2013. Our study is the first to clearly show that mortality related to OsHV‐1 is similar between diploids and triploids in C. gigas when the same germplasm is used for both ploidy. Furthermore, OsHV‐1 resistance was not substantially altered by triploidization, indicating that the achieved selective breeding of diploid oysters for OsHV‐1 resistance can be translated into improved survival in triploids.

Oyster mortality

“…Triploid oysters now represent a significant portion of the oyster production worldwide. It was recently reported that mortality related to OsHV-1 is not affected by ploidy level (Dégremont et al, 2014b), which agrees well with studies conducted on other bivalve species and their pathogens (Smith et al, 2000;Nell, 2002…”

Triploid hard clamsMercenaria mercenariaproduced by inhibiting polar body I or polar bodyII

“…Because of the fast growth, superior meat quality and the ease to produce, “natural” triploids have been commercially produced worldwide. Currently, triploid Pacific oysters account for about 50% of the production in the US northwest coast, and most hatchery produced seed in France (Degremont, Ledu, Maurouard, Nourry & Benabdelmouna, ); triploid eastern oysters account for nearly 100% in Chesapeake Bay in the United States, and that of the Pacific oyster and Sydney rock oyster accounts for about 15% of the production in Australia (Peachey & Allen, ). Triploid production has become an important part of the oyster culture industry worldwide.…”

A literature review as an aid to identify strategies for mitigating ostreid herpesvirus 1 in Crassostrea gigas hatchery and nursery systems

“…Therefore, it has been suggested that either tetraploid lines need to be produced from selected diploid broodstocks or hatcheries need to be provided with the best breeders that have the greatest resistance to OsHV‐1 (Dégremont et al . ).…”

“…Dégremont et al . () found that both diploid and chemically induced triploid C. gigas had similar mortality that could be high using unselected parents or low using parents selected for their higher resistance to OsHV‐1. In Ireland, diploid C. gigas had a greater mortality risk (e.g.…”

“…Therefore, according to the genetic material used, different studies have shown different results and the effect of ploidy is not clear, although Dégremont et al . () suggested that most studies confounded ploidy and family effects, although the absence of OsHV‐1 susceptibility between diploids and triploids has been shown (Azéma et al . ; Dégremont et al .…”