| Freshwater pearl mussel Hyriopsis cumingii, belonging to Mollusca,Lamellibranchiata, Eulamellibranchia, Unionidae, Hyriopsis, is a typical freshwaterpearl mussel in China. It has become the most important freshwater cultured pearlmussels in China due to its several advantageous pearl production traits. In spite of this,the selective breeding program for this species is still shortcoming in the traditionalpearl production industry. The wild stocks are usually collected from lakes, ponds andrivers, reproduced directly and the progeny are used for pearl production. The geneticresource of this species has not been well exploited. The present study aims to have agenetic anlysis of growth rate in three stages and pearl production traits.Three wild populations were collected from the Poyang Lake, Dongting Lake andTai Lake and the healthy parents were used for reproduction. The experiment wasfollowed by nested design. Data were collected three times, i.e. at larval stage, youngmussel stage and pearl production stage. Four traits (shell length, shell height, shellwidth and weight) were measured at each time. To clarify the genetic improvement byindirect selection of pearl production traits, the relationship between these traits andpearl weight were analyzed in this thesis.1．Genetic parameter estimates for growth traits in the early larval stage of HyriopsiscumingiiA total of17half-sib and51full-sib families of H. cumingii were made by nesteddesign. Out of2040individuals in cage,40individuals were randomly selected fromeach of the full-sib families when they reached the size of1cm. Shell length, shellheight, shell width and weight were measured and the data were used for geneticanalysis. The heritability of these four traits was0.356±0.047,0.488±0.060,0.453±0.055and0.518±0.050, respectively. Similarly, the phenotype correlation andgenetic correlation was between0.476~0.709and0.574~0.868, respectively. The high genetic variance for selective breeding in the present study indicated that when we haveselective breeding program on weight, the expected selection response would bemaximum. The other three traits would have some genetic improvement at the sametime.2． Genetic analysis of early growth traitsWhen the individual H. cumingii reached at1cm in shell length, they were movedinto tanks for production. About1000individual were collected randomly form eachplastic box and divided into10replicates. Each replicate was cultured in lantern cageand all of the cages were distributed in the tank by random block design. After57daysof cage culture,30individuals were randomly selected from each cage, totaling of15,300. Four growth traits were measured for genetic analysis in each mussel: shelllength, shell height, shell thickness and body weight. The mean value of these four traitwere3.41cm,1.80cm,0.52cm and2.25g, respectively and the CV were14.60,15.01,23.05and48.83, respectively. The heritability of each trait was0.49±0.37,0.27±0.29,0.59±0.39and0.47±0.38, respectively. Phenotypic and genetic correlation betweenthese four traits fell within the range of0.89-0.95and0.97-1.00, respectively. Earlygrowth traits of H. cumingii showed sufficient genetic diversity for geneticimprovement. There was enough genetic variance in the base population which can beused for selective breeding. Both phenotypic and genetic correlation between the fourtraits were high, thus the modification on one target trait may modify the remainingtraits accordingly. Besides, the result of comparison of the heritability in first two stagesshowed that the heritability was affected by maternal effect in the first and second stage.With the development of the mussel, the maternal effect reduced gradually.3．Genetic analysis of pearl production traitsWhen the individuals in the second experiment reached at least6cm in length,they were prepared for pearl production. All individuals were tagged and shell length,shell height, shell width, weight were measured. A total of501donor and501hostindividuals which were healthy and large enough for operation were randomly selected.The donors were made by spreading section of mantle and transplanted into the mantleof host through horizontal wounds. There were12donors in each side of host. After the donors were prepared, the shells were dried in the shadow. After operation, thedonor’s shells were measured for inside shell color. On Dec2011, the host weremeasured for pearl weight, pearl number, shell length, shell height, shell width, weightand inside shell color (measured on the position L1, L2, L3, R1, R2, R3). The resultsshowed that the mean of pearl weight from host was71.03g with a CV of39.71. Theadditive variance component of this trait was0.63which accounted for0.18±0.09of thetotal phenotypic variance. This result indicated that though the heritability of pearlproduction was on middle level, there would be large genetic gain in this trait becauseof large genetic variance of this trait in the base population.4．Statistical analysis of pearl production parametersThe statistical analysis of pearl production parameters showed that:1) the insideshell color followed a normal distribution and L1>L2>L3and R1>R2>R3;2) there wereno significant difference between two sides of pearl production;3) the CV of the growthrate was42.86with enough genetic variance for selective breeding;4) there wassignificant positive correlation between growth rate and pearl production in the bothsides;5) there was no significant correlation between pearl production and inside colorin the both sides;6) there was no significant correlation between average pearl weightand inside color of the donor’s shell;7) there was no significant effect on pearlproduction by operation system.5．Ranking of better pearl production familiesThe present study showed that the families51#,26#and56#were the highestgrowth rate families whereas the family37#was the lowest growth rate family.Similarly, the families51#,66#and56#were in the front of pearl production. A furtherstudy on marker assisted selection is recommended for the families51#,56#and37#. |
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