Study of the Average Values and Variability of the Basic Productive Indexes of Double, Triple and Tetra-cross Hybrids of Silkworm (Bombyx mori L.)

I. Spring Feeding Season

N. PETKOV, L. IGNATOVA, Y. NACHEVA and P. TZENOV

Sericultural Experiment Station, BG-3000 Vratza, Bulgaria

Abstract

PETKOV, N., L. IGNATOVA, Y. NACHEVA and P. TZENOV, 2000. Study of the average values and variability of the basic productive indexes of double, triple and tetra-cross hybrids of silkworm (Bombyx mori L.). Bulg. J. Agric. Sci., 6: 593-598

A comparative study of the average values and variability of the basic productive indexes of double, triple and tetra-cross hybrids of silkworm was carried out during the spring season of silkworm feeding with the participation of the same parental forms.
The average results for the separate hybrid types show that statistically significant higher values of the basic biological indexes (silkworm viability, yield and percentage of good quality cocoons) and technological cocoon traits (cocoon shell weight and cocoon shell ratio) have been obtained for the complex (triple and tetra-cross) hybrid forms.
In terms of the technological indexes of the silk filament, the double crosses, followed by the triple-cross hybrids have the comparatively longest, thinnest and heaviest silk filament, while tetrahybrids have the relatively lowest values.

In terms of reproductive indexes (number and weight of eggs per laying), the highest values were obtained for the tetra-, followed by triple hybrids and the lowest for double-cross hybrids.
The relatively highest variability of the basic selection indexes (cocoon weight, weight of silk cocoon shell, cocoon shell ratio and length of silk filament) was reported for the tetrahybrids, followed by triple and double hybrids.

Key words: silkworm, Bombyx mori L., tetrahybrids