| Argopecten irradians concentricus has been performed in the Beibu Gulf for more than 20 years.Large-scale breeding has increased the income of local fishermen and promoted the development of the local economy.However,the germ plasm problem is becoming more serious and needs to be solved urgently.In 2005,Professor Liu Zhigang of Guangdong Ocean University introduced and performed cross-breeding the scallop "Bohai Red".The hybrid progeny has obvious growth advantages.Using the method of group breeding,a new scallop hybrid strain called "ZIhaimo" with high temperature tolerance and excellent growth rate was obtained.In this study,its F4 and the local cultured A.i concentricus were used as a control group to conduct a breeding comparison experiment to compare the differences in survival and growth performance between the two group.Based on the growth of its F4 selected lines and non-selected lines,to evaluate the realized heritability of its breeding performence.Comparing the growth performance of F4 and F5 in different seasons,and selecting the most suitable growth model;using molecular marker(SNP)assisted breeding to identify their genetic relationship.In order to provide a Large-scale farming reference basis in Beibu Gulf.1.Growth evaluation of new strain "Zihaimo" F4 and A.i concentricusTo assess the effects of the production performance of the scallop new strain called "Zihaimo" and provide a basis of the breeding effect of the new strain.The research was conducted in the same sea area with the same management mode and breeding cycle.Compared to the seven traits of scallop farming population including shell length(SL),shell height(SH),shell width(SB),body weight(BW),adductor muscle weight(AW)and shell weight(SW)and survival rate of the new strain "Zihaimo" F4 with the A.i concentricus at each stage performance evaluation.The results indicated that the survival rate of “Zihaimo” F4 was 51.32% when it was cultured from October 13 th to April 28 th of the next year and the shell length was from 1～1.5mm to 50～60mm,which was significant(P<0.01)greater than 29.18% of the A.i concentricus.There were significant differences in the shell length,shell height,shell width and body weight of the same population in each month(P<0.05)during the breeding cycle,indicating that the breeding cycle was suitable for the two scallop groups without stagnant growth.However,the shell length,shell height,shell width and body weight of the two groups in the same period had extremely significant differences(P<0.01).It suggested that the growth rate of the new strain was higher than that of the A.i concentricus.After 6.5 months of cultivation,the shell length,shell height,shell width,body weight and adductor muscle mass of the new strain were increased by 19.50%,19.84%,16.23%,56.30% and 20.20%,respectively,compared with the A.i concentricus.2.Growth performance comparison and model fitting of the new strain called "Zihaimo" in different breeding seasonsThe growth performance of the new strain called "Zihaimo" in different cultivation seasons was compared,and the growth models of shell length and body weight in different seasons were fitted in order to provide a basis for the establishment of a suitable cultivation season for the new strain.The results showed that after 6.5months of cultivation in autumn,winter and spring(2019.10.13～2020.04.28),the shell length,shell height,shell width,body weight,adductor muscle mass,shell mass and survival rate of the new strain F4 population were 58.33 mm,55.81 mm,27.14 mm,29.15 g,3.69 g,15.73 g and 51.32%,respectively.After 6.5 months of cultivation in spring,summer and autumn(2020.04.21～2021.11.04),the shell length,The shell height,shell width,body mass,adductor muscle mass,shell mass and survival rate of the new strain F5 population were 49.91 mm,47.46 mm,22.79 mm,21.79 g,2.20 g,9.96 g and 33.64%,respectively.The latter was lower than the former.Various traits was 14.44%,14.96%,16.03%,25.25%,40.38%,36.68% and 34.45%.The results showed that winter farming is better than summer farming.The three growth models of Logistic,Gompertz and Von Bertalanffy were used to fit the shell length and body weight of the population in the two breeding seasons,and it was found that the fit was above 0.988.Combining the actual breeding situation and the model fitting curve,the shell length growth of the new strain called "Zihaimo" can be fitted by Von bertalamffy and Gompertz models,but the model parameters of the same model are different in different breeding seasons;the growth of body weight can be used by Gompertz and Logistic But the model parameters of the same model in different breeding seasons are also different.For the growth inflection point of the same growth model,the inflection point of the shell length in winter is slightly delayed than in summer and the inflection point of the weight in winter aquaculture appears earlier than in summer.The monthly inflection point of the shell length was delayed compared to the body weight,while the growth inflection point of the summer culture body weight was delayed relative to the shell length.After the comparison of the two groups of breeding,it suggested the winter breeding was better than the summer breeding.The research results can provide guidance for the selection of breeding season for new strains,and also provide material for the improvement of scallop breeding theory.3.Contemporary growth performance and realized heritability of the new strain "Zihaimo" F5In the F4 generation of the new strain called "Zihaimo",a comparative study of subsequent selection and non-selection was carried out to investigate contemporary genetic gain and actual heritability.The results showed that the survival rate of the new strain "Zihaimo" F5 was not significantly different from that of the non-selected F5 generation(P>0.05),but there was no significant difference in survival rate(P>0.05),but in terms of shell length,shell height,shell width,body weight,there are significant differences in the quality of adductor muscle,soft mass and shell weight(P<0.05).The traits of the selective breeding group are increased by 3.6mm,3.36 mm,1.3mm,4.82 g,0.67 g,1.82 g and 2.08 g,respectively,compared with the non-selective group.The inheritance of the contemporary traits of the new strain called "Zihaimo" F5,which was successively selected and reached 7.25%,7.13%,5.79%,25.42%,31.60%,27.70% and 21.29%,respectively.The realistic heritability of shell length,shell height,shell width,body mass,adductor muscle mass,soft mass and shell weight were 0.37,0.36,0.30,0.36,0.32,0.38 and 0.32,respectively.The realized heritability of each character of the new strain of "Zihaimo" was high heritability.This study provided the realized heritability of various economic traits for the further selection of new strains,and provided a reference for the heritability of each trait,and also pointed out that the F5 population had the potential for further selection.4.Population genetic structure and genetic identification of the new strain "Zihaimo" and its parentsSimplified genome technology was used to identify the genetic relationship of 96 samples.The average comparison rate of the 96 samples in this study was 96.45%,the average coverage was 13.89%,and the average coverage depth was 5.62X;After filtering according to certain conditions,116 533 SNPs are finally obtained,with an average of 13.43 SNPs detected per 100kb(effective length),and used for subsequent population analysis and subsequent population structure analysis.The evolutionary phylogenetic tree showed that the A.i concentricus clustered into one,the scallop "Bohai Red" clustered into one cluster,the hybrid progeny clustered into one cluster,and the Chlamys farrela cluster clustered into one cluster;when K=4,the cross-validation error rate was the smallest,the optimal number of subgroups was determined to be 4,indicating that these samples may come from four ancestors after germ plasm differentiation;principal component analysis(three-dimensional map)shows that the outer group was relatively far away from the other three subgroups,and the scallop "Bohai Red".The distance between the group and the A.i concentricus was closer to the hybrid F5 group,which was consistent with the results of the evolutionary tree.The SNPs before the three populations were filtered according to the conditions of deletion greater than 0.5 and MAF>0.5 to filter the hybrid F5 population,and finally 338 SNPs were obtained.These SNPs were distributed in 158 Contigs,with an average of 2.2 SNPs per contig,of which Contig155 has up to 10 SNPs.The parental genotype transformation yields a conversion to transversion ratio is1.19.In summary,the F5 population of the new strainstrain "Zihaimo" is indeed the offspring of the scallop "Bohai Red" and A.i concentricus. |
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