| Owing to poor resources of shrimp germplasm, culture environmental degradation and so on, this study concentrates on new variety breeding of Litopenaeus vannamei to carry out the following several researches. Comparative analysis of difference in major economic traits of F1 generation, such as growth, survival, resistance, high temperature resistance, low salt, high ammonia resistance, low dissolved oxygen, and so on, was carried out on the way of diallel cross. Based on the developmental genetic model, the genetic effects for body weight at different growth stages in L. vannamei were analysed.According to growth, survival and resistance to low dissolved oxygen traits for selection index, parent groups which have a significantly genetic diversity on the F1 generation were selected and used to establish a large number of family groups for the founder population,for estimating genetic parameters of growth traits in founder population at different growth stages and analysis of interaction of genotype and environment. The main conclusions showed as that:1.Analysis on Combining Ability of Survival of Imported L. vannamei Populations by Temperature and Salinity Stress9 populatuions showed significant differences for tolerance to temperature and salinity stress. The advantage range of Hybrids resistant to high and low temperature, high and low salinity traits in mid-parent heterosis respectively are:-17.71~52.95,-22.04~77.03,-39.41~76.96,-44.89~37.05, and these ranges of heterobeltiosis respectively are:-30.07~37.96,-33.93~31.17,-42.12~19.07,-45.68~28.21. The highest average to high temperature in mid-parent heterosis were UM and UH groups, which was 38.61%, while the highest average to low temperature were UM and TZ groups, which was 60.85%. The general combining ability of parents and special combining ability of hybrid combinations together influenced the tolerance performance of hybrid offspring, in which the UM group had higher general combining ability in resistance traits with high and low temperature,while TZ group had higher general combining ability in resistance traits withIV high and low salinity. The specific combining ability analysis showed that UM×UH was strong hybrid combination, which has stronger non additive effect and hybrid superiority,and could provide candidate materials for further family selection.2.Analysis on Combining Ability of Survival of Imported L. vannamei Populations by Ammonia Nitrogen and Dissolved Oxygen StressThe results showed that 9 groups showed significant differences in tolerance to dissolved oxygen, ammonia nitrogen stress. The advantage range of Hybrids resistant to high ammonia nitrogen and low dissolved oxygen traits in mid-parent heterosis were14.09~42.57 and-52.48~31.39, respectively, while these ranges of heterobeltiosis were1.860~26.18 and-54.34~24.66, respectively. The general combining ability of parents and special combining ability of hybrid combinations together influenced the tolerance performance of phybrid offspring, in which UH group had higher general combining ability in resistance traits for high ammonia nitrogen and low dissolved oxygen, which was0.1442 and 0.0899 respectively. The specific combining ability analysis showed that UM×UH was strong heterosis combination, which has stronger non additive effect, and could provide candidate materials for further family selection.3.Evaluation of Growth Performance in Three Imported L. vannamei Populations and Hybrid OffspringThe results showed that the ranges of least squares means of 9 mating combinations at three stages were 5.86~12.15 g, 14.79~28.82 g and 38.25-54.74 g, respectively, which least squares means of hybrid combinations were higher than inbred combinations. The ranges of specific growth rate were 3.40-5.70%, 1.11-2.56% and 0.33-0.68%, respectively.Heterosis analysis showed, positive mid-parent heterosis and heterobeltiosis were observed for body weight of hybrid combinations at three stages with diminishing trend. The highest heterosis occurred in the hybrid offspring crossing Miami population as female parents and Hawaii as male parents. At each growth stage, least squares mean of offspring of Miami population were higher than the average of these 3 parents populations. Miami population as parent was relatively excellent and the M-H and M-T were optimized cross combination.4.The Dynamics of Genetic Analysis of Body Weight with Time Series in L.vannavmeiThe unconditional additive variance component of body weight had an increase trend along with the growth and development in shrimp and was 8.856 and 24.114 at adult shrimp and broodstock shrimp, respectively. Unconditional dominance variance component and unconditional additive variance component presented different genetic expression for body weight at different developmental stages, showing a different geneticexpression. Unconditional dominance variance of body weight was increased in aberdeen shrimp, adult shrimp and adult shrimp, but decreased in broodstock shrimp. Unconditional additive variance accounted for 8.062%, 0.9765%, 11.308% and 24.636% at the same stage of the total phenotypic variance. Cumulative effect for body weight main caused by dominant effect gene expression, particularly in the early stages of growth and development.Conditions genetic effects analysis showed that the new expression of genetic effect can be found at four development stages in shrimps. The net additive effect of new expression had an increased trend and condition additive variance component estimates of body weight traits were 0.07567±0.0101, 0.270944±0.0342, 14.013±0.4847, 25.68467±1.3631 at 0|BW1, BW2|BW1, BW3|BW2 and BW4|BW3 four growth and development interval. However, the net dominance effect of the gene effects for new expression within a time interval expressed fluctuant and has expression actively during BW2|BW1(14.4198±0.9616). Genetic variance components accounted for 0.630696, 0.640384, 0.151975 and0.0381932 of the total phenotypic variance at same stage.5.Genetic Parameters Estimates for Growth Traits in Founder Population of L.vannameiThe estimated heritability(h2) for BL(0.0778-0.4149), HL(0.0117-0.5061),DL(0.1289-0.4808), HW(0.0624-0.5348) and BW(0.1535-0.4867) in two livestock farm was low to moderate at different stage of L.vannamei, including postlarval stage, adult prawn stage and harvest stage. The common effect(c2) at three stage ranged from 0.0093 to0.1679. The genetic correlation among growth traits ranged from 0.0177 to 0.6113. The result showed genetic correlation for BW was 0.3477, 0.1775 and 0.2344, for DL was0.1160, 0.1202, 0.2140 and for BW was 0.2453, 0.2352, 0.2394 respectively, between three different stage(including postlarval-adult prawn stage, postlarval-harvest stage and adult prawn-harvest stage), but genetic correlation between three different stage in L.vannamei was no statistically significant different from zero in this study. The heritability(h2) and common effect(c2) for same growth trait between two livestock farm had little difference and was not significantly different from zero by Z-score(P>0.05). The genetic correlation among all growth traits between two livestock farm was significantly different from zero by Z-score(P>0.05). |
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