Effect of selection of cocoon filament length in divergently selected lines of the silkworm, Bombyx mori

Abstract

To examine the effects of selection and the degree of manifestation of heterosis, we compared the polyvoltine populations of Bombyx mori selected for long or short cocoon filament lengths for 11 generations, and performed their inter se matings and crosses of selected lines with unrelated bivoltine tester populations. We measured the selected trait, viz. the filament length, as well as other unselected traits such as survival rate, single cocoon weight, cocoon shell weight, cocoon shell ratio and filament size. The genetic improvement brought about for filament length by virtue of selection was found to be reflected in the hybrids. On an average, genes for short filament length were found to be dominant over those of long filament length. Significant difference in reciprocal crosses was observed for the selected trait in the interline matings. Matings of the lines with long or short filament lengths with the unrelated tester population reflected the filament length of the selected population. Among the unselected traits, heterosis was more extensive for the survival rate followed by the single cocoon weight and cocoon filament size in both interline matings and the crosses of the selected lines with unrelated tester population.