Investigation of Inbreeding Effect on Economical Traits of Cocoon in Ten Commercial Silkworm lines of Iran

A total of 22268 records from 10 commercial silkworm lines reared in Iran Silkworm Research Center including Chinese lines of 32, 104, 152, 110 and 154 and Japanese lines of 31, 103, 107, 151 and 153 collected during 3 years in 4 rearing periods in spring and autumn were used for study of effect of inbreeding on economic traits. Two statistical models were used for analysis of the data. In the first model, inbreeding coefficient was considered as a covariate variable along with fixed effects of line, rearing year and season. In the second model, inbreeding effect considered as a classified fixed effect along with other mentioned fixed effects. All effects had highly significant effects (P0.0001) on all traits. However, the non-significant effect of inbreeding on cocoon shell weight in the first model was an exception. Tukey-Kramer test was used for comparison of means. The means of different levels of each fixed effect were significantly (P 0.01) different for all traits. In the first model, partial regression coefficients on inbreeding were significant for cocoon weight (P< 0.0001) and cocoon shell percentage (P< 0.01) and not-significant for cocoon shell weight. The results of this study showed that increasing of inbreeding significantly increases the cocoon weight and decreases the cocoon weight percentage, but its effect on cocoon shell weight is not significant. Regarding to the results of this study, it could be concluded that increasing of inbreeding has no noticeable effect on silk quantity. Therefore, increasing of inbreeding, at least, at the studied level of this population, is probably acceptable.