Genetic analyses and breeding strategy for silkworm races of different cocoon filament size

Abstract

This research focused on the genetic analyses of cocoon filament fineness and its use for breeding silkworm races that have characteristics of cocoon filament fineness. Based on two kinds of Chinese parent silkworms (Bombyx mori), the results of the experiment showed that cocoon filament size had a positive interaction on cocoon shell weight and the ratio of cocoon shell weight, but it had a negative interaction on cocoon filament length. Moreover, the hybrid vigor rate was high in association with crop yield, cocoon shell weight, and cocoon filament mass.
However, examination against other characteristics showed that hybrid vigor was weakly associated with cocoon filament size, and had moderate association with cocoon weight, percentage of cocoon shell weight, and cocoon filament length. The curves plotted for estimated and measured cocoon filament lengths and sizes of F₁, F₂ and BF₁ showed similarities. This result suggests that it is possible to make predictions about several hybrids based on estimations drawn from the parent silkworm specimens. In addition, it was clarified that the size curve of cocoon filaments reflected an average of the parent silkworms. Therefore, this breeding strategy for silkworm races, of the thin cocoon filament, can meet the recent demands posed by various sides of the silk industry. This is because silk companies, sericulture farmers and egg production companies primarily base their selection preferences on cocoon filament fineness and cocoon filament length, followed secondarily by hybrid vigor or cocoon crop yield, etc.