| The blunt snout bream?Megalobrama amblycephala,MA?is an important freshwater cultured fish in China,with an annual output of about 800,000 tons.Distanthybridization can combine the excellent traits of parents and rapidly promote the formation of new species by forming new genotypes and phenotypes for fish breeding.Hybrids contains two or more different genomes,usually shows heterosis in terms of fast growth rate,increased genetic diversity,improved muscle quality,et al.However,the heritability of ideal hybrid will be gradually lost with the transmission of generations,Backcross has been widely used in aquatic breeding by breeders to consolidate excellent traits and stabilize genetic characteristics.In addition,the escape of fertile hybrid offspring will pose a great threat to natural germplasm resources,In fish breeding,hybrid and triploid breeding methods can be combined,which can not only enable hybrid progeny to obtain comprehensive heterosis of parents,but also obtain sterility characteristics of triploid.The energy of triploid for gonad development is transferred to growth and meat quality improvement,which also opens up a new method for fish breeding research.Artificial crossbreeding technology was introduced into M.amblycephala?MA??×C.alburnus??CA?.On this basis,backcross?BC1?BC2?was carried out with M.amblycephala and C.alburnus as female parents respectively,and a new line population of heterodiploid hybrid?F1-F4?and backcross?F1-F3?was obtained.In this study,the hybrid F2?MC-F2?,backcross F2?BC1-F2?BC2-F2?and their original parents of M.amblycephala and C.alburnus were taken as experimental objects,and the following three aspects of growth performance,genetic structure and triploid induction research of M.amblycephala hybrid and backcross were carried out,which laid a solid foundation for the research of M.amblycephala and C.alburnus fish breeding.?1?Five breeding populations were constructed,including Megalobrama-amblycephala?MA?and Culter alburnus?CA?,M.amblycephala?×C.alburnus??MC-F2?,M.amblephala?×?M.amblycephala?×C.alburnus????BC1-F2?and C.alburnus?×?M.amblycephala?×C.alburnus????BC2-F2?,the growth performance and muscle nutrition quality of the five populations were analyzed,and the taste analyzed by electronic tongue.The observations suggested that,compare to the original parents,BC1-F2 groups has the most significant growth advantageand similar measurable shape to female parent,anddisplayed high protein content and low water leve1?P<0.05?.Further analysis of Amino acid revealed than the total amino acid,total essential amino acid and flavor amino acid of BC1-F2 were higher than their original parents?P<0.05?.The total essential amino acid amount and the total amino acid amount are 17.54%and 6.92%respectively.Electronic tongue analysis showed that the tastes of the five fishes were obviously different,and the tastes of the two crossed offspring were all partial to their recurrent parents.Comprehensive analysis results show that BC1-F2 has not only remarkable growth performance but also effectively improved muscle quality to a certain extent compared with its parents,and has more breeding potential.?2?The genetic structure of hybrid progeny of M.amblycephala and C.alburnus was studied by microsatellite analysis of five populations.The mean value of number of alleles?Na?of MA?CA?MC-F2?BC1-F2?BC2-F2 were 5.25,4.40,4.75,4.85and 5.10,respectively,The mean value of observed heterozygosity?Ho?is 0.8117,0.5550,0.7967,0.8317 and 0.6200 respectively,The mean value of expected heterozygosity?He?is 0.7095,0.6329,0.6995,0.7240 and 0.6915 respectively,and the average value of polymorphism information content?PIC?is 0.6557,0.5717,0.6406,0.6676 and 0.6339 respectively.The mean Hardy-Weinberg indices of MA,MC-F2,BC1-F2 displayed a heterozygote excess,whereas the gynogenetic populations?CA and BC2-F2?showed a het-erozygote deficit.The unweighted pair-group method with arithmetic means?UPGMA?showed than the CA and BC2-F2 popuations first grouped together,and than MA and BC2-F2 first grouped together,and then they clustered with the MC-F2.According to the genetic identity analysis,F2hybirds and backcross F2groups showed maternal effect.Particularly,the microsatellite primers Me.Am.?15?Me.Am.?1?TTF01 and Mam25 identified five groups.The results are of great significance to the conservation of germplasm resources,the identification of population and the selection of improved varieties for the hybrid offspring of M.amblycephala.?3?A new hybrid M.amblycephala and C.alburnus strain with fast growth,high meat quality and sterility is produced.In this study,three induction conditions including hydrostatic pressure treatment start time,treatment intensity and treatment duration were set up to induce the triploid of M.amblephala?×?M.amblycephala?×C.alburnus????BC1-F3?,and the best induction conditions for inducing BC1-F3triploid were obtained.BC1-F3 triploid was induced by hydrostatic pressure method.The triploid induction effect was the highest with a triploid rate of 9.67%when the incubation temperature was 22 0.5?and the treatment was carried out 3min after fertilization,and the pressure was 50MP and the pressure was 3 min.Chromosome analysis showed that karyotype and fundamental number were determined to be 3n=72,3n=24m+36sm+12st,NF=132 in triploid,2n=48,14m+28sm+6st,NF=90 in control group.In this study,a certain proportion of triploid BC1-F3 can be obtained by inducing BC1-F3 fertilized eggs by hydrostatic pressure method,but the overall induction rate is extremely low.The triploid rate has been increasing but not decreasing at 50MP.Follow-up research on BC1-F3 triploid induction can continue to optimize the pressure intensity and add the condition of different pressurization time to obtain the best induction effect. |
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