Evolution of new productive bivoltine hybrid CSR3 x CSR6

Earlier breeding experiments (1970's) have yielded productive hybrids with a cocoon shell ratio of 18% at commercial level. These hybrids have not made much impact in the field. There is a need to shift production to superior quality and quantity of silk. The experience with bivoltine silk production, on the whole is not very encouraging. Farmers have not realized bivoltine hybrid rearing as very remunerative and rewarding. Keeping this in view, reorientation in breeding approaches has been envisaged. Of late, the adoption of bivoltine sericulture in India gathered momentum being armed with the evolution of a good number of robust and productive bivoltine breeds/hybrids of silkworm, Bombyx mori L. for tropical conditions. The breeding work was initiated in this Institute by utilising two Japanese hybrids namely BN18 x BCS25 and Shunrei x Shogetsu along with Indian evolved breed, CC1. The breed CSR3 which is characterised with sex-limited larval marking and white oval cocoons was evolved from the Japanese hybrid BN18 x BCS25 by crossing with CC1, while the breed CSR6 which is characterised with normal marking (marked larvae) and white dumbbell cocoons was extracted from the Japanese commercial hybrid Shunrei x Shogetsu through continuous inbreeding coupled with selection. After fixation, these breeds along with other newly evolved breeds were subjected for hybrid study under optimum environmental conditions in the laboratory for expression of full potential of the genotypes. These hybrids were evaluated by the Evaluation Index Method (Mano et al., 1993). Seven productive hybrids were short-listed and the hybrid CSR3 x CSR6 is one among then. The hybrid CSR3 x CSR6 recorded a survival of 94.1%, a shell weight of 50.2 cg, a shell ratio of 24.5%, a raw silk percentage of 19.8, a filament length of 1295 m and a renditta of 5.1. On the other hand, the control hybrid (KA x NB4D2) has recorded a survival of 90. 6%, a shell weight of 42.1 cg, a shell ratio of 20.4%, a raw silk percentage of 15.9, a filament length of 999 m and a renditta of 6.3. The hybrid CSR3 x CSR6 was authorised by the Central Silk Board in the year 1999 for commercial exploitation during favourable months