Study on the Heterosis and its Components in Hybrids between Monobivoltine and Polyvoltine Strains of Silkworm (Bombyx mori L.) with Reference to the Cocoon Yield Characteristic

Y. NACHEVA, P. TZENOV and N. PETKOV
Regional Center of Applied Scientific Services, Sericulture Experiment Station BG - 3000 Vratza, Bulgaria

Abstract

NACHEVA, Y., P. TZENOV and N. PETKOV, 2005. Study on the heterosis and its components in hybrids between monobivoltine and polyvoltine strains of silkworm (Bombyx mori L.) with reference to the cocoon yield characteristic. Bulg. J. Agric. Sci., 11: 93-98

The purpose of the investigation was to determine the heterosis effect in F1, the depression in F2, the degrees of dominance in F1 and F2 and the gene effects involved in the inheritance of the "cocoon yield per box of silkworm eggs" character.
It was found that almost all examined hybrids between the monobivoltine strains Vratza 35 and Merefa 2 and polyvoltine tropical strains Cambodia, Bonde 517 and Daizo exhibited a relatively high heterosis effect in F1 compared to MP and negative values of heterosis compared to HP.
The degrees of dominance indicators in F1 (hp1) and F2 (hp2) show that heterosis with regard to the "cocoon yield per box of silkworm eggs" character is due in most cases to intermediary inheritance (-0.5 < hp1 < +0.5).
An important part in the genetic control of the "cocoon yield per box of silkworm eggs" character is played by the epistatic gene interactions of the type dd and ad, as well as by the dominant gene effects (d), which are positive and produce an increase in the character values.

Key words: Silkworm (Bombyx mori L.); hybrid; cocoon; cocoon yield; silkworm eggs; heterosis; depression; degrees of dominance; gene effects