Cocoon Shape Inheritance in Hybrids between Multivoltine and Uni-Bivoltine Silkworm, Bombix mori L. Races

P. TZENOV, Y. NACHEVA and N. PETKOV

Sericultural Experiment Station, BG-3000 Vratza, Bulgaria

Abstract

TZENOV, P., Y. NACHEVA and N. PETKOV, 1999.Cocoon shape inheritance in hybrids between multivoltine and uni-bivoltine silkworm, Bombyx mori L. races. Bulg. J. Agric. Sci., 5: 457-456

A study with the Bulgarian uni-bivoltine lines Super 1 and Hessa 2, the Tropical multivoltine race Bonde 517 and their F1, F2 and BF1 crosses have been undertaken. The cocoon shape inheritance expressed as the so called "cocoon index" was investigated in the study.
The results obtained indicated that in the F1 heterosis expression with respect to the BP value was detected as for the cocoon size and an itermediate inheritance of the cocoon index character was observed in F1.
The variation factor (VC) of the cocoon length, width and index characters was lower in F1 and the BF1's with the uni-bivoltine lines and the variation factor values were higher in the F2 and BF1's with the multivoltine race.
It was determined that 70.76 % of Bonde 517 cocoons had cocoon index from 1.60 to 2.00 in 90.32 % of Super 1 cocoons the index was from 1.70 to 2.10 and 96.72 % of Hessa 2 cocoons had cocoon index from less than 1.30 to 1.60.
In the F2 of the crosses Hessa 2 x Bonde 517 and reciprocal average 85.71% of the cocoons had cocoon index from 1.50 to 1.90 in 5.77% the cocoon index was less than 1.50 and in 8.53% the cocoon index was higher than l.90.
In BF1 with Hessa 2 91.57% of the cocoons had cocoon index from 1.30 to 1.70, while in the BF1 with Bonde 517 76.83% of the cocoons had cocoon index from 1.60 to 2.00.
The cocoon shape inheritance in the uni-bivoltine x multivoltine crosses studied is controlled by polygenic aditive gene actions.

Key words: silkworm, Bombyx mori L., cocoon shape, cocoon index, inheritance, uni-bi x multivoltine crosses