Correlation Between Genetic Similarity And Heterosis For Growth And Reproductive Traits In Oujiang Color Common Carp

Complete set line breeding, initiated in animals since1950-1960, is one ofbreeding methodology to product special mating combinations withsignificant heterosis by using “special lines” containing novel economicaltraits. By now, the complete set line breeding has been widely used indomestic animal and crops, such as pig, poultry, wheat, corn. However,this breeding method has not been used in fish.Oujiang color common carp （Cyprinus carpio var. color） is a widespreadvariant of common carp found in the Oujiang River basin of ZhejiangProvince, and it has been locally cultured in rice paddies and yards formore than1200years. According to color, it can be classified wholered（WR）, whole red with big black spots（RB）, whole red with small blackspots（RS）, whole white with big black spots（WR）, whole white（WW）. Theplentiful color patterns like this fish is rarely found in freshwater fish inChina, which make it have very important role in Chinese biodiversity.Since1999, we have conducted the study on genetic diversity and completeset line breeding in Oujiang color common carp, and have achievedimportant advances on these fields. In this study, correlation betweengenetic similarity and heterosis for growth and reproductive traits werestudied for the five complete set lines of Oujiang color common carp byusing combined methodologies of molecular and quantitative genetics, andstatistics, which may be useful in providing theoretical basis for completeset line breeding in fish. 1.Correlation between genetic similarity and heterosis for growth traitsin Oujiang color common carpThe complete diallel crosses with25mating combinations were made from5complete set lines in Oujiang color common carp （Cyprinus carpio var.color）. Three kinds of microsatellite DNA Markers （nSSR, EST-SSR,QTL-SSR） were used to analyze genetic similarity （Genetic distance andfixation indices） in the parental lines. Then, correlation was investigatedbetween genetic similarity and phenotypic values, heterosis of growth traitsin25combinations （e.g.body weight, total length, standard length,pre-dorsal height and pre-dorsal width）. The result showed that there weresignificant difference （P＜0.01） in allelic richness （A_R）, observedheterozygosity （H_O） and inbreeding coefficients (F_IS) of parents amongthree kinds of molecular markers, but no significant differences （P＝0.57）in expected heterozygosity （H_E）. there were significant correlations（r=0.401－0.404; P=0.03-0.04） between body height, body width andgenetic distance （GD） from QTL-SSR, and no significant correlations（r=-0.05－0.390；P>0.05） between the other growth traits and geneticdistance of SSR markers. Similarly, there were no significant correlations（r=-0.10－0.21; P>0.05） between the growth traits and genetic divergence（FST）. No significant correlations （r=-0.11－0.44；P>0.05） were foundbetween heterosis and genetic distance, genetic divergence from threemarkers. Principal component analysis （PCA） for breeding lines indicatedthat EST-SSR may be more better and fitter than the other two markers topredict the correlation between heterosis of growth traits and geneticdifference of breeding lines. 2. Combining ability detection and correlation analysis of heterosis andgenetic similarity for reproductive traits.The complete diallel crosses of F1were made from5complete set lines inOujiang color common carp （Cyprinus carpio var. color）.Additive-dominance mixed genetic model was used to analyze thecombining abilities（SCA, GCA） and heterosis of the six reproductive traits,including male gonadosomatic index （M_GSI）, female gonadosomaticindex （F_GSI）, absolute fecundity （AF）, relative fecundity （RF）,fertilization rate （FR） and hatching rate （HR）. Meanwhile, correlationanalysis was conducted between heterosis of reproductive traits and geneticsimilarity（Genetic distance, GDand divergence, FST） of three kinds of SSRmarkers （nSSR, EST-SSR, QTL-SSR）. The results showed that obviousdifferences were found among reproductive traits in different matingcombinations. The highest F_GSI and HR were found in combinations that“whole red with small black spots”（RS） of Oujiang color common carpwas used as maternal parent，the highest AF and RF were observed incombinations that “whole red”（WR） of Oujiang color common carp wasused as maternal parent, however, relatively low values of reproductivetraits were detected in combinations that “whole white with big blackspots”（RB） of this fish was used as maternal parent. The phenotypiccorrelations among F_GSI, AF and RF were significantly positive（r=0.411-0.847，P=0.01-0.04）. Specific combining ability （SCA） wassignificantly detected in F_GSI, AF and RF. Ten combinations weredetected with predicted specific combining ability （SCA） and heterosis （H）.Additionally, significant correlation existed between SCA and heterosis intraits of M_GSI, F_GSI, AF, RF and HR （r=0.959-0.985, P<0.01）. therewas significant correlation （r=0.425，P=0.03） between GDfrom EST-SSR and M_GSI, and no significant correlation （r=-0.158-0.436； P>0.05）between the other GDand reproductive traits. similarly, there were nosignificant correlations （r=-0.158-0.314， P>0.05） between FSTof allmarkers and reproductive traits.