| In the world market, China produces most of the freshwater pearls. However, dueto the low quality of the pearl, the Chinese pearl output value occupies a small share ofthe total world pearl value. There are obvious gaps between the freshwater pearl qualityand international market requirements. Pearl color is one of the main factors thatdetermine the quality and price of pearls, and studies have shown that the nacre pearlcolor of H. cumingii providing a small piece of mantle cell directly affects the color ofpearls. H. cumingii is a characteristic freshwater pearl mussel and an importantfreshwater pearl mussel in China. The selected line of H. cumingii F4was produced in2009by selection breeding for four generations with the indexes of the purple innershell color and body weight. In this study, the parental mussels of breeding group werefrom the selected F4of purple H. cumingiii, and the parents of control group wereunselected. The comparisons of the inner shell color and growth traits between the twogroups were made to evaluate the selection effect. And Microsatellite-based DNAparentage analyses were used to assign offspring to their family to establish full-sibfamilies. Heritabilities, genetic correlations and phenotype correlations for inner shellcolor and growth traits were estimated using REML method during one year old stage.Mainly included the following contents:1Evaluation of Selection Effect for F4In order to evaluate the selection effect, six families were established respectivelyin the breeding group with the selected line as parents and the control group withordinary population as parents, marked with B1-B6and C1-C6. The comparisons of the inner shell color and growth traits between the two groups were made. Results showedthat the inner shell color of breeding group were all purple, the total color differencevalue dE*which integrated color parameters L*, a*, b*, denoted the color differencebetween the sample and the standard white. The dE*of the breeding group was verysignificantly different from the control group (P<0.01). It was10.0%higher than thecontrol group. The differences of growth traits between groups were also verysignificant (P<0.01), shell length,shell height, shell width and body weight of thebreeding group was higher7.5%,11.4%,4.7%,17.9%than the control group,respectively. The coefficients of variation of growth traits in the breeding group were alllower than the control group. The variation coefficients of shell length, shell width,body weight, decreased by22.5%,8.5%,18.3%,27.1%, respectively. The resultsindicated that the selection lines were improved over generations and the effect ofbreeding was prominent. The inner shell color of F4had been purified, and the growthrate were significantly improved and tended to be more consistent.2Parentage assignment based on microsatellite markersThis study was initiated to assess the feasibility of parentage determination inaquaculture populations for Hyriopsis cumingii. Seven microsatellite markers wereemployed to identify the parentage relationship for four matrilineal pedigrees, whichwere produced by mass breeding. The polymorphic information content (PIC) of sevenmicrosatellite markers ranged from0.576to0.842, with the average of0.722. The rangeof variation of the expected heterozygosity and the observed heterozygosity were0.631～0.861and0.708～0.839, respectively. The number of allele at each loci was5～13, and the average was8.5. The results showed that the seven marks were all highlypolymorphic, and they could guarantee the accuracy of the identification. When noparent information or only one parent information was available, the combinedexclusion probability for seven loci was98.4%and99.9%, respectively. Further simulations based on allele frequencies suggested that more loci than eight wererequired for parentage assignment to achieve the exclusion probability of99%when noparent information was available and five microsatellite loci were required when onlyone parent information was available. With the occurrence of multiple paternity in H.Cumingii,10sires were detected for all progeny, ranging from2to4in each matrilinealpedigree. But the paternal contributions to offspring showed large difference. Thereexisted a dominant sire, with the highest contribution rate. The contribution rates of thedominant sire for the offspring of four matrilineal pedigrees were82.2%,77.8%,71.1%,82.8%, respectively, and the other sires had a small contribution rate, ranging from4%to18%. These results provided important technical support for analysis of relationshipand family selection based on microsatellite markers in Hyriopsis cumingii.3Estimates of genetic parameters for inner shell color and growth straits during oneyear old stageSix polymorphic microsatellite markers were employed to identify the maleparents of offspring from15female parents of the purple strain F4of Hyriopsis cumingiiParentage assignment showed that42full-sib families from12male parents and15female parents were obtained. Heritabilities, genetic correlations and phenotypecorrelations for inner shell color and growth traits were estimated using REML methodduring one year old stage. The heritability estimates of the color parameters L*, a*, b*,dE*were0.31±0.22,0.11±0.08,0.36±0.18,0.29±0.19, respectively. The geneticcorrelations and phenotypic correlations of L*, a*, b*were low, with the range of0.08~0.47and0.04~0.32, but the correlations between L*and dE*were very high(rg=-0.94±0.06, rp=-0.96±0.01). The heritability estimates for shell length (0.24±0.19),shell height (0.37±0.27), shell width (0.26±0.16), wet weight (0.26±0.17), and shellweight (0.31±0.19) were moderate and high. A positive and high genetic correlationsand phenotypic correlations were found among growth traits (rg=0.71~0.92,rp=0.66~0.94). The genetic correlations and phenotypic correlations between the color parameters and growth traits were very low, ranging from0.02to0.18. The resultsshow that most of the heritabilities of color parameters and growth traits were moderateand high, suggested that this strain should respond rapidly to selective breeding. Mutualselection couldn’t be achieved due to the very low correlations between inner shell colorand growth traits, and the body weight should respond to targeted selection with thehigh phenotype correlations and genetic correlations with other growth traits. Therefore,selective breeding for inner shell color and body weight was a reasonable decision toimprove inner shell color and growth traits. |
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