Evolution of bivoltine silkworm hybrids of bombyx mori L under hill conditions

Abstract

The objective of this breeding study, was to amalgamate desirable traits available with a group of potential bivoltine genetic resources possessing attributes on fitness, productivity, fibre quality and shorter larval duration through appropriate selection of breeding resource materials, adopting specific breeding and selection strategies and by undertaking systematic hybrid evaluation so as to develop and identify superior bivoltine hybrid combinations possessing the desired targeted traits on productivity (shell percentage gt22) along with relatively shorter larval duration (around 22 days). Thirty one bivoltine silkworm genetic resources available at Satellite newlineSilkworm Breeding Station, Coonoor when subjected for evaluation studies employing multiple trait index and index scoring method, had resulted in identification twelve potential parental resources. Amalgamation of desired traits on fitness, productivity, fibre quality and shorter larval duration was attempted in selective fashion and by adopting productivity index suggested by Gamo, (1976) along with keeping a minimum of 30% female population in selected batches. Ten new SLD breeds developed after breeding process, when subjected for hybrid evaluation, heterosis studies, estimation of silk productivity (Gamo, 1976), measurement of cocoon uniformity, assessment of reproductive potential had resulted in the development of six new breeds, SLD1, SLD2, SLD4, SLD6, SLD8 and SLD9; Of which, SLD4 and SLD8, are marginally superior to CSR2 and CSR4 in productivity merits and relatively shorter larval duration (20 hours (SLD4), one day twenty hours (SLD8) less); One new single hybrid, SLD4 x SLD8 with shorter larval duration (18 hours less) and marginally superior productivity traits than the control, CSR2 x CSR4; Six new foundation crosses, SLD1 x SLD2, SLD2 x SLD4, SLD3 x SLD4, SLD5 x SLD9, SLD8 x SLD9 and SLD9 x SLD10; Of which SLD2 x SLD4 and SLD8 x SLD9, are marginally superior to CSR2 x CSR27 and CSR6 x CSR26, in productivity merits and with shorter larval