Combining ability of seven silk technological characters in mulberry silkworm, Bombyx mori

The combining ability (abbreviated, CA) effects of five races (KA, CC1, CA2, NB4D2 and NB18) of mulberry silkworm Bombyx mori and their 20 F-1's, including reciprocals, were analyzed in a 5x5 diallelic crossing system for the following seven silk technological characters: cocoon weight, shell weight, cocoon shell ratio, raw silk percentage, silk filament length, silk reelability and silk neatness. The parental race CA2 did not show the best general CA for any of these seven characters, whereas the other parental races did for different characters as follows: race KA for raw silk percentage, silk filament length, silk reelability and silk neatness; race CC1 for cocoon weight, shell weight, and cocoon shell ratio; race NB4D2 for cocoon weight, raw silk percentage; race NB18 for cocoon shell ratio. Values of race CA2 for general CA were negative for cocoon weight, shell weight, cocoon shell ratio and raw silk percentage, and were low for silk filament length, silk reelability and silk neatness. This indicated a poor performance of this race in hybrid combinations with the remaining races. The results of specific CA effects suggested the restricted use of race CA2 as a female parent in hybrid combinations with males of races NB18 or NB4D2. Crosses CA2 x NB4D2 and CA2 x NB18 showed the desired positive specific CA effects for all characters except silk reelability and silk neatness, respectively. Cross CC1 x NB4D2 showed desired positive specific CA effects for all characters. Variances of general and specific CA revealed that the non-additive type of gene control plays a predominant role in the inheritance of all the seven characters analyzed. The races and crosses showing best values of general and specific CA effects will be used in future breeding programmes.