POSIBILITIES FOR USING SILKWORM STRAINS WITHOUT PIGMENTATION OF EGG SEROSA IN BREEDING NEW SEX-LIMITED FOR EGG COLOR SILKWORM BOMBYX MORI L. BREEDS

Abstract

The silkworm sex-limited for egg color breeds available in the national germplasm of Bulgaria
have too low productivity and viability and because of this they haven’t been used for commercial hybridization. In the silkworm sex-limited for egg color breeds the eggs with female embryo have graygreen serosa color while those with male embryo have colorless serosa, thus their color is yellow. This peculiarity allows when cross females of sex-limited for egg color breeds with males of colorless egg serosa breeds to preserve the sex limitation in the next generations. In the present study the breed 1
A 1, which is the only one without egg serosa pigmentation available in Bulgaria, but having too low productivity was used. This breed had been mated with the silkworm breeds Super 1 and Hesa 2 and by a subsequent breeding work two new highly productive strains, called Milena 1 and Milena 2 and without egg serosa pigmentation were created. Males of the Milena strains have been mated with females of sex-limited for egg color breeds E 18, E 21 and E 22, using the back-crossing method. The results obtained manifest that the productivity and viability of the initial sex-limited for egg color breeds have gradually been improved, thus we recommend the method for usage in the breeding practice.