Detecting and verifying microsatellite markers associated with disease resistance in cultured populations of eastern oysters, Crassostrea virginica

The eastern oyster, Crassostrea viginica, is an economically important aquaculture species in the USA, but several diseases, such as Dermo and MSX, inhibit maximum production. Efforts have been made to develop disease-resistant oyster lines using selective breeding techniques based on phenotype; however, achievement of the desired trait is hindered by the inability to maintain consistent and intense selection pressure in field trials. Marker-Assisted Selection (MAS) offers an effective alternative to traditional breeding techniques by selecting based on genetic markers associated with disease resistance, even in the absence of disease-related selection pressure. The greatest challenge in applying MAS is to identify markers that are consistently associated with the disease-resistant phenotype. In this study, 20 previously published microsatellite markers, including 9with some prior evidence of association with disease resistance were used to genotype and compare oyster populations of the same stock (NEH-RI) deployed at two sites (York River, Virginia and Cape Shore, New Jersey) before and after a disease-caused mortality period (March – November 2013). One marker (RUCV 270) with prior evidence of association with disease resistance exhibited significant shifts in allelic distribution post-selection at both sites. Two additional markers with prior evidence of association (Cvi2i23 and RUCV 97) exhibited significant post-mortality allelic distribution shifts in one site but not the other. Lastly, significant differences in allelic distribution before and after selection were detected in one marker (RUCV 68) with no prior evidence of association with disease resistance at both sites. These results strengthen the evidence associating markers RUCV270, Cvi2i23 and RUCV97with the disease-resistant phenotype and suggest that marker RUCV68 warrants further investigation. Additional genetic and functional genomic analyses are required to determine whether these markers are suited for MAS