Character Analysis Of A New Variety Named "Shen-zhe NO.1" In Sinonovacula Constricta And Screening Of SNP Loci For High Temperature Resistance Related Genes

Sinovacula constricta is an important economic shellfish along the coast of China.It is an important guarantee for the healthy and sustainable development of industry to cultivate fast-growing and stress-resistant new varieties.in the process of genetic breeding of S.constricta,the reproductive biology of 1-and 2-year-old S.constricta was studied by the effective accumulated temperature rule and histological method.Selection of juvenile and parent shellfish by path analysis and correlation analysis.Screening of optimum hybrid combinations by complete diallel hybridization.Screening SNP loci of ScHsc70 gene related to high temperature tolerance.The results are as follows.1?According to the rule of effective accumulated temperature and the linear regression method,the biological zero was confirmed by histological analysis of the total gonadal development cycle.The results suggested that the biological zero of gonadal reproduction of 1-year-old and 2-year-old S.constricta was the equal,which is 20.8?C.When the temperature reached to 20-21?C,the histological sections indicate that more than half of the S.constricta individuals initiated gonadal development.The average effective accumulated temperature for two years is 802.60 d??C.This study would contribute us to understanding of the regulation and control of gonadal maturation,suggesting that changes in the season of spawning and breeding during one-year farming of the new variety razor clams could provide an economic benefit to industrialized spat production for a new variety of razor clam in the large-scale.The results demonstrated the razor clam S.constricta is a typical clam of accumulative temperature mature oviposition type.In addition to,it is not a type of hypothermy but needing lower temperature to its gonadal mature and spawing.2?Then results showed that the correlations among the qualitative characters were reached extremely significant levels.The shell length showed the greatest correlation coefficients to the live weight of the 4-month age and 11-month age?0.911 and 0.631?respectively.However,the shell height showed the greatest correlation coefficients to the weights of the 9-month age?0.653?.The result of the path coefficient analysis showed that the highest path coefficients were the shell length?0.562?,shell width?0.433?,and shell height?9.394?at 4^th,9^th and 11^th month age,respectively.The results of the determinant coefficients were consistent with the results of the path analysis.The multiple regression equations were obtained to estimate live weight of S.constricta as 4^th,9^th and11^th month age weights?W?:W₄=-0.756+0.039 SL+0.112 SW,R²=0.849;W₉=-10.622+0.095 SL+0.404 SH+0.644 SW,R²=0.631;W₁₁=-23.772+0.207 SL+0.805SH+0.587 SW,R²=0.909.3?In order to breed a new strain of sinonovacula constrictor with fast growth and high temperature resistance.Complete diallel hybridization was carried out using three different geographical culture populations from Zhejiang?Z?,Fujian?F?,and Guangdong?G?province,china.The larval and spat growth and the survival and heat resistance of spat were compared in detail.By means of the serial growth traits at larval and spat measurements?shell length and shell height?,the experimental result indicated that there was no difference between six hybrid crosses and those of parental crosses at larval stage,while at spat stage some differences were observe.It was noted that the hybrid crosses ZF?Z?×F??,ZG?Z?×G??and FG?F?×G??outperformed the parental groups at the end of intermediate culture in shell length,which were 21.77±0.28 mm,21.55±0.29mm,21.44±0.20 mm,respectively.For spats survival rate,the hybrid cross ZF?Z?×F??was significantly larger than all the other groups,which was 88.89±4.16%and that of the hybrid cross ZG?Z?×G??was significantly larger than the cross GZ?G?×Z??and parental crosses ZZ?Z?×Z??and GG?G?×G??.The hybrids crosses ZF?Z?×F??,ZG?Z?×G??and FG?F?×G??exceeds the parental groups in heat resistance,but there was no significantly difference.Considering the growth,survival and heat resistance,the results concluded that the crosses ZF,ZG and FG in this study were deemed to be the better hybridization combinations for genetic improvement,which could have significant implications for the development of razor clam aquaculture.It is basis that provide a theoretical for breeding new varieties with fast growth and high temperature tolerance.4?In this study,the full-length sequence of ScHsc70 gene was cloned by direct sequencing.The length was 4 048 bp,including 6 introns and 7 exons,and the coding region was 1 950 bp.Under heat stress high temperature resistance groups and control groups from a new variety of razor clam were established six potential SNPs Rs1?g.588C>T?,Rs2?g.840 C>T?,Rs3?g.885 T>A?,Rs4?g.1233 A>G?,Rs5?g.1467 T>G?,Rs6?g.1482 T>C?were screened from the exon region of ScHSc70 gene by PCR product direct sequencing.SNPs genotyping was performed on the high temperature tolerant population and the control population of the new variety“Shenzhe No.1”by Sanger sequencing.The results of genetic diversity analysis showed that the polymorphism information content?PIC?of the two populations was between 0.111 2 and 0.371 8,and the average polymorphism information content of the control population was 0.267 0,which is higher than that of the high temperature resistant populations?0.223 65?.Association analysis results showed that the genotype frequency and allele frequency of Rs1,Rs3 and Rs4 were significantly different between control group and high temperature tolerant group.Haploid linkage disequilibrium analysis showed that SNPs markers of ScHsc70 gene could form 2 haploid blocks and 7 haplotypes,among which CCT haplotypes were significantly correlated with high temperature tolerance traits?P<0.05?.It was found that Rs2 and Rs3 were in a linkage state?r²=0.86,LOD=25.56,D=1.0?,and could be used as SNP markers for the Genetic breeding of S.constricta for high temperature tolerance.In summary,Rs1,Rs3,Rs4 and haplotype CCT can be used as candidate auxiliary molecular markers for high temperature tolerance breeding of razor clam,which lays a theoretical foundation for the subsequent functional verification of resistance-related SNPs.