Effect of Selection Index on Resistance of Silkworm F1 Hybrids to Nuclear Polyhedrosis Virus

This experiment was conducted to determine the effect of selection index in four iranian commercial silkworm lines (107, 110, 153, 154) on resistance of their hybrids including 107×110, 110×107, 153×154, 154×153 under stress of nuclear polyhedrosis virus (N.P.V) Infection. Selection index program was performed on 3P commercial lines during 9 generations. Later generation parents of 3P lines were selected in each generation, by forming selection matrix based on heritability parameters, correlation between cocoon weight, cocoon shell weight and cocoon shell percentage and phenotypic mean of traits. In the 10th generation, 2P populations (produced by random cross of 3P) were mated randomly and P (parent) silkworm eggs were produced by random mating of 2P population. P populations in selected and random groups were reared in village conditions (growths silkworm rearing house silkworm). Control P population was produced by crossing 2P population (produced by non-selected 3P lines). F1 hybrids of control group (non-selected) were reared simultaneously. From the obtained results, the hybrids of 110×107 and 154×153 significantly showed the highest performance for individual cocoon traits (P<0.05).The best cocoon percentage, middle cocoon percentage, low cocoon percentage, double cocoon percentage, total cocoon weight, larva survival rate and pupation rate were studied, that showed negative relationship between resistance and production characteristics. The results demonstrated that selection index method have a negative effect on resistance of silkworm hybrids as well as improving production and economic performance of silkworm hybrids. It is recommended that economical coefficients and genetically parameters are estimated for productive, resistance and quantitative cocoon characters together. Then parents would be selected on the basis of those parameters.