Study on the Heterosis and Its Components in Hybrids between Monobivoltine and Polyvoltine Strains of Silkworm (Bombyx mori L.) with Reference to the Shell Weight 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, 2004. Study on the heterosis and its components in hybrids between monobivoltine and polyvoltine strains of silkworm (Bombyx mori L.) with reference to the shell weight characteristic. Bulg. J. Agric. Sci., 10: 741-744

An investigation was conducted 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 shell weight characteristic in monobivoltine and polyvoltine silkworm hybrid combinations. A pronounced heterosis effect was found in F1 compared to MP for hybrids produced with the polyvoltine strain Bonde 517 as a parent, while the rest showed negligible or negative heterosis effect. Compared to HP, the heterosis effect was negative. The heterosis in F1 compared to MP, manifested with regard to shell weight characteristic, is due to intermediary inheritance (hp1= from -0.31 to +0.34). The inheritance of the character is conditioned to a relatively highest extent by the dominant-dominant (dd) and additive-dominant (ad) epistatic gene interactions. It is recommended to use the polyvoltine strain Bonde 517 as a gene donor in selection programs in order to improve the tolerance of newly evolved strains of silkworm to adverse rearing conditions.

Key words: silkworm (Bombyx mori L.); silk shell; hybrid; heterosis; depression; degrees of dominance; gene effects