SNP Fingerprinting for Germplasm Identification of the Fast-Growing Pacific oyster (Crassostrea gigas) "Haida No. 1" Variety

The Pacific oyster (Crassostrea gigas) is a global aquaculture species of economic significance. Selective breeding programs have been conducted to produce multiple strains with fast growth as well as other desirable traits. However, due to the phenotypic plasticity of oysters, challenges existed for precise germplasm identification among selectively bred strains. In this work, we identified selection signatures of three fast-growing Pacific oyster strains originated from wild populations collected from China, Japan, and Korea, respectively, which were used for development of SNP-based molecular fingerprinting for precise identification of germplasm. We performed whole-genome resequencing of 59 oysters from three selectively bred strains and a wild population for genome-wide SNP analyses. Population structure analysis with these SNPs revealed significant genetic differentiation among the selectively bred strains. Based on the FST index, we identified 41, 49, and 36 strain-specific SNPs from the three selectively bred strains. Taking into account the "hitch-hiking effect" that occurs in the genome during positive selection, we identified two, three, and two molecular fingerprints for the three strains, respectively. We validated the molecular fingerprints of the China selectively bred strain (i.e., "Haida No. 1" variety) with a separate population of 42 oysters with diverse genetic background, demonstrating the accuracy of germplasm identification of over 96%. This work provides a reliable tool for precise germplasm identification of the "Haida No. 1" variety as well as other two selectively bred strains, which is valuable in germplasm conservation and breeding design in the C. gigas.