Development Of Multiplex PCR Of Microsatellites And Studies On Genetic Parameters Of Growth Traits In Pacific Oyster(Crassostrea Gigas)

The Pacific oyster Crassostrea gigas is one of the most important worldwide aquaculture species, ranking first in production comparing with other aquatic species. However, the broodstock used still is wild or cultured which is unselected in many oyster hatcheries.Therefore, to develop a fast growth, high resistance C. giga is the main task of the selective breeding program, and it’s also one of the most effective way to solve these problems.In this study, we establishtwo sets of high-level 5-multiplex to be used for rapid and efficient parentage assignment in C. giga. However, it’s the first time to estimate shell-closing strength for C. giga. In addition, this is the first to apply mixed-family approach combined with a partly factorial design in C. giga. Both genetic parameters and G × E interactions were analyzed with a mixed linear model and restricted maximum likelihood(REML) using ASReml-R. These provide basic data and theory reference for germplasm improvement and new caltivar breeding of C. giga.1. Development of multiplex PCR of microsatellites and it’s application to analysis in C. giga.We tested two sets of high-level 5-multiplex PCRs for efficient genotyping in C. giga. Ten loci were selected based on polymorphism, reliability, and allele size range. They were divided into two groups according to allele size and labeled with four different fluorescence dyes, so that loci in the same color was not be overlap in size. In addition, we performed a paternity test for 27 full-sib families and 643 offspring of Group 0527 and 27 full-sib families and 382 offspring of Group 0612 with software CERVUS 3.0. Parentage analysis demonstrated that 100% of all offspring were allocated unambiguously to the unique pair of parents when two sets of 5-multiplex PCRs were used for Groups 0527 and 0612. The assignment success for the two groups was 96% based on MS 1(the first 5-multiplex PCR). However, the assignment success was 97% and 95% based on MS 2(the second 5-multiplex PCR) for Groups 0527 and 0612 respectively. Therefore, the two sets of 5-multiplex PCRs can be used for rapid and efficient parentage assignment in C. giga.2. Estimation of genetic parameters for growth traits in C. giga.The heritability for seven traits is shell height(SH, 0.24 ± 0.09), shell width(SW, 0.11 ± 0.07), shell length(SL, 0.35 ± 0.15), wet weight(WW, 0.37 ± 0.16), meat weight(MW, 0.31 ± 0.14), adductormuscle weight(AMW, 0.36 ± 0.14) and shell-closing strength(SS, 0.25 ± 0.13). Heritabilities for all traits ranged from 0.11 to 0.37, and most of them were medium-high except shell width.All of genetic and phenotypic correlations were significant and positive. Genetic correlations between them all were medium-high, ranged from 0.53- 0.99. Thevariationrangeof phenotypic correlations between different traits was larger than genetic correlations. The lowest was 0.10 and the largest was 0.81. In addition, together with the high heritability of shell length, we can use length instead of wet weight and meat weight as a selection criterion in a C. giga breeding programme which is much easier to measure. Likewise, the selection breeding of adductor shell-closing strength can implement the breeding of muscle weight indirectly.3. Estimation of G × E interactions for growth traits in C.gigas.The significant genetic correlations were high for shell height, shell length, meat weight and adductormuscle weight, indicating that selection in one environment tended to gain similar genetic response in another environment. However, both genetic correlations forwet weight and shell-closing strength were small(<0.8), which meant the effect of genetic-environment interactions was strong. Therefore, G × E interactions had important impact on the design of wet weight and shell-closing strength selective breeding which could set up site-specific breeding programs.