| Pacific white shrimp（Litopenaeus vannamei）is the most important shrimp cultured species in China.Recently,nine new varieties of L.vannamei have been cultivated in China,but compared with the introduced species from abroad,they are not competitive to meet the demands for diversified environment and various breeding modes in China.The reasons,first,mostly family breeding and population breeding are used in selection of new shrimp varieties,rarely with the research and application of hybrid breeding,which results in insufficient utilization of heterosis;second,the genetic improvement of the stress resistance of new shrimp varieties in China is mostly based on a single factor,while in the practical breeding production,it is often under the three factros-stress of multiple environmental factors.A new variety with a specific excellent stress resistance is extremely unstable in the diversified breeding environment.Therefore,this study constructed a family with domestic and foreign excellent L.vannamei as parents to evaluate the genetic parameters of growth and three factros-stress tolerance traits.The results are as follows:（1）Evaluation of genetic parameters of growth and three factros-stress tolerance of L.vannamei G9generation80 full-sib families have been established,38 full sib families were finally retained.After 60 days of breeding in the same environment,the genetic parameters of growth and three factros-stress tolerance of L.vannamei at the age of 15 weeks were estimated by multi trait animal model.The results showed that the growth traits were high heritability（0.37±0.09）～（0.51±0.10）,and the three factros-stress tolerance traits were medium heritability（0.21±0.06）,indicating that it is feasible to improve the growth and three factros-stress tolerance traits;The genetic correlation of growth traits was generally high（0.54±0.13）～（0.99±0.01）（P<0.01）;which indicates that any growth character can be replaced by others for indirect selection;The genetic correlation between growth and three factros-stress tolerance traits showed a low to medium positive correlation（0.11±0.23）～（0.39±0.19）,indicating that the three factros-stress tolerance traits can also be indirectly improved when breeding with growth traits as the main selection target.（2）Analysis of hybrid combining ability of growth and three factros-stress tolerance of L.vannamei G9generationTaking five populations of L.vannamei with different genetic backgrounds as parents,12 F1generations of combinations were constructed by mating.After 60 days of breeding in the same environment,the hybrid combining ability（GCA and SCA）of growth and three factros-stress tolerance(high salt（35）,low p H（6±0.1）and high ammonia nitrogen（70mg/L）at the age of 15 weeks were estimated by asreml4software.The results showed that the hybrid combination GX♀×W♂had the highest body mass SCA（0.31±0.22）and heterosis（25.52%）;Hybrid combination W♀×GX♂had the highest three factros-stress tolerance SCA（1.30±2.03）and higher heterosis（41.72%）.It can be considered to strengthen the hybrid application of the two combinations in growth and three factros-stress tolerance traits respectively.（3）Evaluation of additive and dominant genetic effects of growth and three factros-stress tolerance at two growth stages of L.vannameiUsing 6 populations of L.vannamei with different genetic backgrounds as parents,60 full sib families（including 29 half sib families）were constructed.Four unisexual animal models were used to estimate the additive and dominant genetic effects of growth and three factros-stress tolerance at two growth stages.The results showed that A+C model was more suitable for genetic evaluation of 7-week-old and15-week-old growth and three factros-stress tolerance traits.In addition,the 7 traits of7 weeks old were mainly additive effects,and the 7 traits of 15 weeks old were mainly dominant effects except three factros-stress tolerance,head breastplate length and head breastplate width.It suggested that selection breeding is better for genetic improvement of the growth traits and three factros-stress tolerance traits of 7 weeks old shrimp;Selective breeding is more suitable for genetic improvement of the three factros-stress tolerance traits and cross breeding is more suitable for genetic improvement of the growth traits of 15 weeks old shrimp.（4）Genetic correlation analysis of growth and three factros-stress tolerance traits and 4 stress traits of L.vannamei in G10generationThe genetic parameters of growth and three factros-stress tolerance of L.vannamei at 7 and 15 weeks old were estimated by animal model.The results showed that the heritability of growth traits was medium to high（0.256±0.119）～（0.441±0.124）,and the heritability of three factros-stress tolerance traits was low（0.029±0.034）～（0.053±0.058）,which indicating that it was feasible to improve growth by selection;The genetic improvement of three factros-stress tolerance traits needs the method of family and intra family selection for multi generation breeding.The genetic correlation between growth and three factros-stress tolerance traits in age was positive but low（0.081±0.129）～（0.224±0.125）,indicating that the selection of growth traits will have a certain positive correlation response to three factros-stress tolerance traits.The results also showed that there was a relatively low genetic correlation between growth traits at different ages（0.285～0.342）（P<0.05）,which indicated that the early selection of growth traits of L.vannamei might not be the best and should be selected at the later stage.In addition,there was a significant positive correlation between the comprehensive stress tolerance and the high ammonia nitrogen stress tolerance（0.355）and high salt stress tolerance（0.403）respectively,indicating that breeding for the comprehensive stress tolerance traits of L.vannamei could simultaneously improve resistant to high ammonia nitrogen stress and high salt stress. |
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