Three way crosses between two-band red and white zebra strains of Manila clam,Ruditapes philippinarum

In order to improve the phenotypic character of Manila clam Ruditapes philippinarum,three way crosses between Two-band Red(R:fast growth)and White Zebra strains(WZ:obvious heterosis)were conducted in August 2009.The generation F2 of White Zebra strain was from two way crosses between Pearl White and Zebra strains.The experiments consisted of two self-fertilized groups(RR,WZWZ)and two hybrid groups(RWZ,WZR).Then the growth,survival,heterosis and shell color genetic mechanism were investigated in the study.The results showed that the single-parental heterosis was asymmetrical between two reciprocal crosses,and the growth and survival were clearly improved in RWZ group,whereas only survival heterosis was observed in another group.Considering growth,the value of mid-parental heterosis was -0.68,and that of single-parental heterosis was +1.70 for RWZ,and -2.92 for WZR,respectively.It was mainly affected by the interaction between egg origin and mating strategy,next is maternal effect during planktonic stage.The value of mid-parental heterosis was only +0.90,and that of single-parental heterosis was +9.71 for RWZ,and -6.57 for WZR during juvenile stage.Considering survival,the value of mid-parental heterosis was +3.60,and that of single-parental heterosis was +4.47 for RWZ,and +3.05 for WZR,respectively.It was mainly affected by the mating strategy,next that is maternal effect during planktonic stage.The value of mid-parental heterosis was +9.00,and that of single-parental heterosis was +13.09 for RWZ,and +7.30 for WZR during juvenile stage.The shell color of generation for R×R,R×WZ,WZ×R,WZ×WZ were two band red,two band red with white zebra,two band red with white zebra and white zebra,respectively.The generation of white zebra was still white zebra on the outer shell color,that is,no shell color separated for two way hybrids.These results indicated that coloring was linked to sex and was not of sex-linked inheritance.