EVOLUTION OF NEW FOUNDATION CROSSES OF BIVOLTINE SILKWORM HYBRIDS UNDER SEMI TEMPERATE CONDITIONS OF NILGIRIS
The breeding of new varieties and races are very much essential to cope up with the demand from and also for the survival of any agriculture and allied industries. The main objectives of silkworm breeding are to increase productivity, to enhance disease resistance and to improve quality. In addition, the other specific aims and areas of importance are fecundity and survival, more cocoon yield, minimum defective cocoons, good reelability, uniform filament and neatness. The primary goal of silkworm breeding is the cumulative improvement of the desirable traits. Scientific breeding methods coupled with the application of basic principles of Genetics have enabled the silkworm breeders to evolve new genotypes with desirable characters. The breeding of inbred lines by crossing between two strains with desired characters and thereby selection for the traits such as healthiness of larvae, egg productivity, cocoon uniformity and yield, quality of filament were targeted.
Twenty nine newly evolved bivoltine pure breeds maintained at the germplasm stock of Satellite Silkworm Breeding Station of Central Silk board, Coonoor, sixteen oval breeds and thirteen dumbbell breeds, were selected as resource material for the study. The breeds were reared in two seasons, studied their efficiency on rearing and reeling performance based on fourteen cocoon and silk yield parameters; seven each of pre-cocoon, viz., fecundity, fifth age larval duration, total larval duration, pupation rate, single cocoon weight, single shell weight, shell percentage and post cocoon traits - average filament length (AVFL), non breakable filament length (NBFL), denier, renditta, reelability, and neatness. Using these bivoltine breeds (viz., sixteen oval cocoon breeds viz., CSR 2, D1, D2, D 7, CSR 202, CSR 204, CNR 5, CNR 14, CNR 15, SLD 1, SLD 2, SLD 4, Gen 1, Gen 3, CSR 50 and thirteen dumbbell cocoon breeds - CNR 3, SLD 6, SLD 8, SLD 9, D 11, D 13, D 15, D 17, GEN 2, 4 C, CSR 6, CSR 26, CSR 51) forty seven new foundation crosses were prepared in P.O. x P.O (Plain larvae & Oval cocoons) and M. D. x M.D (marked larvae & dumbbell cocoons) fashion among them in all possible combinations of direct crosses. Two Foundation Crosses- FC1 (CSR6 x 26) for dumbbell foundation crosses and FC2 (CSR 2x 27) for oval foundation crosses were kept as control and evaluated the rearing performance of 49 FCs (47 new FCs and 2 control) for two seasons. Analyzed the data on rearing and reeling parameters and short listed them to 14 Foundation crosses for further evaluation and preparation of double hybrids.
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