Analysis of Expression of Heterosis on Fecundity, Hatchability of Eggs in New Breeding Lines of Bombyx mori L

The present study was designed to evolve bivoltine races for our tropical climatic conditions by utilizing the silkworm races of known genetic background (KA, NB18 and PM) in different hybrid combinations and to inbreed them over generations followed by backcrossing and adopting appropriate selection at different generations with an objective of the viability and productivity. The isolated bivoltine lines (R1 and R2) were reared in different seasons of the year along with their parental races to evaluate their stability in the expression of commercial characters such as fecundity and hatchability. The pure races of bivoltine Kalimpong-A (KA) spinning oval white cocoons, New Bivoltine-18 (NB18) spinning dumbell white cocoons and multivoltine Pure Mysore (PM) spinning pointed yellow cocoons of mulberry silkworm Bombyx mori L. were selected for the present breeding programme. Single and three way crosses were made by using the above said three races. The first single cross involved KA females and PM males. The second single cross involved NB18 females and PM males. During the course of breeding selection was made at the egg, larva, pupa and cocoon stages to fix the desirable traits. F5 progenies of the respective crosses were back crossed to their respective bivoltine males to improve commercial characters. Heterosis in F1 generations of crosses including NB18 and PM were determined over Mid-parental value (MPV) and Better parent value (BPV). Significant test for heterosis was performed using standard analysis of variance (ANOVA) table. Based on the results of our study it was concluded that the metric variables like fecundity and hatchability are found to be complexly related being influenced by the physiological conditions of an organism also.