Comparison of different multi-trait selection strategies for genetic improvement of economic traits in six Iranian commercial lines of the silkworm, Bombyx mori (Lep.: Bombycidae)

In this study, the genetic parameters and economic weights of some important economic traits in six Iranian commercial varieties (110, 107, 101433, Xinhong1, Koming1 and Y) of the silkworm were estimated and selection indices for these traits constructed. Individual recording of cocoon weight, shell weight and shell ratio were carried out during six generations. Heritabilities and genetic correlation between traits were estimated by restricted maximum likelihood method. The heritability of cocoon weight and shell weight were higher than that of shell ratio. Genetic improvement of cocoon weight and shell weight were high in the line 101433 due to higher heritability and genetic correlation between them. Therefore, the restriction of genetic gain of cocoon weight in this line is expected to cause a severe decrease in improvement of shell weight, and subsequently a decrease of selection efficiency. The genetic improvement of cocoon shell percentage increased in restricted indices due to low genetic correlation with cocoon weight, and selection accuracy in these indices decreased significantly compared to other indices. Considering the difference in genetic parameters and economic values of traits in commercial lines of the silkworm, it would be necessary to define a separate breeding goal and selection strategy in each line.