Combining ability analysis of seven silk yield attributes in silkworm, Bombyx mori L.

The combining ability effects of five silkworm (Bombyx mori L.) strains and their 20 F₁'s including reciprocals were analysed in a 5x5 diallel cross for seven silk yield attributes, viz. effective rate of rearing (ERR), a measure of survival, cocoon yield, cocoon weight, shell weight, raw silk percentage, silk filament length/cocoon and silk reelability. Higher values of specific combining ability (SCA) than the corresponding general combining ability (GCA) for all the attributes except ERR and cocoon yield are indicative of non-additive gene action. The parental strain JC2P was the best general combiner for all the attributes, except cocoon yield. The highest general combining ability effect for cocoon yield was shown by N4. The highest desirable or positive SCA effects resulted from N4 × SH2 (all the attributes except shell weight), JC2P × 14M (all the attributes except cocoon weight and shell weight), 14M × SH2 (all the attributes except ERR), N4 × SPJ1 (all the attributes except shell weight and raw silk percentage). Only one reciprocal, namely SPJ1 × N4, showed positive effects for all the attributes except silk reelability. The improvement of cocoon yield through mass selection followed by intermating and the use of the parental strain JC2P in future cross breeding are discussed.