Identification and mapping of disease-resistance QTLs in the eastern oyster, Crassostrea virginica Gmelin

Identification and mapping of disease-resistance QTLs (quantitative trait loci) is important for our understanding of genetic mechanisms of disease-resistance and for our ability to genetically improve cultured stocks. Disease-resistance is the most important trait for farmers of the eastern oyster (Crassostrea virginica Gmelin), which is affected by two major diseases: MSX and Dermo. In this study, the genome of the eastern oyster was scanned with a large number of amplified fragment length polymorphism (AFLP) markers before and after Dermo-inflicted mortalities (53% and 67%) in two reference families. Significant post-mortality shifts in genotype frequency were detected at a large number of loci. Linkage analysis revealed that most markers showing frequency shifts are closely linked to each other on the genetic map, and all markers within a cluster had frequency shifts in the same direction according to their linkage phase. This finding suggests that post-mortality shifts in genotype frequency were not random, but linked to Dermo/summer mortality-resistance QTLs. Twelve putative Dermo/summer mortality-resistance QTLs were identified on female and male maps from two families, providing candidate genome regions for further analysis.