| Pinctada fucata is an economically important oyster that is cultured for pearl production in China. However, with the addition of the effect of inefficiency cultivation methods and environmental pollution in cultivation, the growth and the mortality of P. fucata is decreasing and increasing, repectively, it had serious influence the quality and yield of the pearl in China. It is important to improve the growth and the resistance to disease of P. fucata by the method of genetic improvement.The mainly of this study is to evaluate the genetic of the growth traits and resistance to Polydora ciliata in the pearl oyster Pinctada fucata, results of analysis mentioned above are as following:1. Using grey relational analysis method to examine the relationship between shell traits and body weight in 12 selective breeding families of P.fucata. The results showed that the means of body weight, shell length, shell height, shell width and hinge length were 35.96 g, 57.36 mm, 59.24 mm, 23.55 mm and 56.93 mm. The coefficients of variations in body weight and shell traits ranked as follows: body weight(21.30%) > shell length(9.91%) > hinge length(9.12%) > shell height(8.85%) > shell width(8.30%). Based on grey relational degree, the grey relational degrees between each shell traits and body weight were calculated and ranked as follows: shell height(0.7459) > hinge length(0.7148) > shell width(0.7059) > shell length(0.6825). The results showed that the values of shell height had the closest relationship with body weight. So the shell height could be used as an important factor for the evaluation of P. fucata breeding practice for high growth lines selection and the improvement of selection efficiency.2. Use SANYA, SHENZHEN and VIETNAM three different group cultured Pinctada fucata as parents to make complete diallel cross and built 9 mating combinations(3 selfing combination groups and 6 cross combination groups), whose heterosis and combining ability of body weight, shell weight, viscera weight, adductor muscle weight and resistance to Polydora ciliate were analyzed. The results showed that, total heterrosis of the body weight, shell weight, viscera weight, adductor muscle weight and resistance to Polydora ciliate were 11.36%, 7.88%, 14.02%, 11.20% and 53.95%, respectively. The largest mid-parent heterosis of body weight in the 6 cross combination groups is SANYA×SHENZHEN, the mid-parent heterosis is 29.28%, 21.27% higher than SANYA group and 38.41% higher than SHENZHEN group. However, the largest mid-parent heterosis of resistance to Polydora ciliate is SANYA×VIETNAM, which the mid-parent heterosis is 81.82%, 33.33% higher than SANYA group and 185.71% higher than VIETNAM group. The general combining ability effects of SANYA group, which is the best in body weight, viscera weight, adductor muscle weight and resistance to Polydora ciliate were 0.7132, 0.7939, 0.1281 and 0.0282, respectively. The specific combining ability effects of SHENZHEN×SANYA in body weight, shell weight, viscera weight, adductor muscle weight and resistance to Polydora ciliate are the highest. We also found that, the reciprocal cross group of SANYA×SHENZHEN, the heterosis of both in weight traits and on the resistance to Polydora ciliate were greater than the orthogonal group, and on the phenotypic value, except the adductor muscle weight rank only second to the orthogonal group of SANYA×SHENZHEN, all traits of the reciprocal cross group of SANYA×SHENZHEN in all groups were greatest and significantly different from zero(P<0.05).We suggest that, when used SANYA and SHENZHEN group as parents to make hybridization, in order to improve the efficiency of breeding, we should use SANYA group as sire and SHENZHEN group as dam.3. A two-trait animal model and a sir-dam threshold model were used to estimate the variance components and genetic parameters for traits of growth and resistance of Pinctada fucata to Polydora ciliate. The results showed that the heritability estimates for shell width and body weight were high(0.3850±0.1421 and 0.3478±0.1292, respectively) and were significantly different from zero(P<0.05) indicated by LRT test. There was a high phenotypic and genetic correlation between shell width and body weight(0.935 and 0.883, respectively) and were highly significantly different from zero(P<0.01). Heritability of resistance to Polydora ciliate was high(0.3387±0.1316) but not significantly different from zero(P>0.05). The phenotypic correlation between family growth(shell width and body weight) and resistance to Polydora ciliate were 0.260 and 0.152, respectively, and the genetic correlation between family growth(shell width and body weight) and resistance to Polydora ciliate were 0.233 and 0.083, respectively, showing low correlation(r<0.30) and no significant difference from zero(P>0.05).The higher heritabilities of shell width, body weight and resistance to Polydora ciliate suggested that the three traits have high potentials for selective breeding, but the low correlation between growth traits and resistance demonstrated that when taking the shell width or body weight as a breeding goal, the resistance to Polydora ciliate cannot be effectively improved in the same time. Therefore, it is necessary to use a multiple traits selection method to selectively breed a new strain of P. fucata with fast growth and high resistance.4. Variance components and heritability of resistance to Polydora ciliate were estimated using two different trait definitions(binary trait and categorical trait) and five statistical models(linear model-binary trait, threshold(probit) model-binary trait, threshold(logit) model-binary trait, threshold(probit) model-ordinal trait and threshold(logit) model-ordinal trait).Heritability of resistance to Polydora ciliate in different statistical models range from 0.3322±0.0943~0.5764±0.1352, all of them were higher heritability.The result of correlation coefficients between the predicted family breeding values from two replicated tanks and accuracy of selection in different statistical models showed that, the threshold(logit) model-ordinal trait is the most suitable model to estimate genetic parameters for resistance to Polydora ciliate, which the correlation coefficients between the predicted family breeding values from two replicated tanks is 0.896, and the accuracy of selection is 0.947. |
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