Breeding oysters resistant to herpes virus

A project that uses genetic markers identified family differences in farmed oyster pacific oyster for resistance to herpes virus. Two genetic markers explained about half of the genetic variation for survival against the virus. The knowledge can help an industry select oysters effectively and efficiently to improve survival.

Background

The Pacific Oyster (Crassostrea gigas) is a very important seafood species, comprising about 98 percent of global oyster aquaculture. Infectious diseases pose a significant threat to sustainable production, with high economic losses due to deaths.

Ostreid herpesvirus type 1 (OsHV-1) is highly contagious, with a relatively short life cycle and can cause up to 100 percent deaths in septic oysters. Juvenile oysters (2-5 cm / 5-20 g) are much more receptive than adult oysters (> 5 cm /> 20 g). Outbreak is characterized by a reduction in feeding and swimming activities, along with sudden high mortality rates. OsHV-1 virus can infect several other conch species – including blue thigh, European flat oyster, wedge shell and kingfisher – showing the robustness and adoptability of OsHV-1 in a wide range of hosts, and making it very threatening ever detected in a system.

Genes influencing survival

The analyzes, conducted by scientists from Nofima and Ifremer, found family differences for resistance to OsHV-1 virus. Therefore, some families have shown better survival than others and the choice of individuals (as parents of the next generation) from resistant families using genetic markers would effectively improve survival against OsHV-1 explosion.

The results produced in this study are part of an EU-funded project VIVALDI (program H2020, n ° 678589). The oyster population was produced by a specific F2 a cross, originating from the breeding core of Ifremer, in France, by the mixing of resilient and receptive grandparents. The study used a sample opportunity after a natural field explosion of OsHV-1 in the sea.

Approach

At the end of the OsHV-1 outbreak, the collected tissue samples from the dead and the surviving individuals were selected in equal numbers, in a bid to increase the power to detect genetic signs influencing the survival against the virus.. The selected shellfish were genotyped using a 40,000 single-nucleotide polymorphism (SNP) table (Thermo-Fisher, AXIOM). The data (survival phenotype and genotype) were analyzed to detect SNP markers and / or quantitative trait sites (QTL) associated with the survival versus OsHV-1, which led to the detection of two significant genomic regions.

Effect

The two markers (the main marker of each region) accounted for about 50 percent of the genetic variation for survival. OsHV-1, and therefore can help industry select oysters effectively and efficiently to improve survival OsHV-1. The effect of the detected markers is similar to markers identified against cardio (CMS) and the pancreatic (PD) diseases in Atlantic salmon, which are now used / adopted as markers / QTL products in the salmon farming industry. Hence the QTL markers identified for survival OsHV-1 has strong potential for the Pacific oyster industry.

Jean-Baptiste Lamy, an Ifremer scientist, is very pleased with the findings. He believes that the results of this study on genetic variation, and the results of QTL, which explain large proportions of genetic variance, will convince oyster companies to implement more carefully designed breeding programs, and test advanced – but relatively capital intensive and effective – solutions, such as marker assisted and / or genomic selection. In addition, the results of this study should inspire more studies on other complex diseases caused by Vibrio aesturianus, and the simultaneous infections between viruses and bacteria that threaten global oyster production.

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