Genetic Variability and Relationship among Cocoon Traits in Japanese Lines of Silkworm Bombyx mori L.
Genetic parameters and economic values of some important traits in three Japanese commercial silkworm varieties (107, 101433 and 153) were analyzed and selection indices for these traits were constructed. Individual recordings on cocoon weight, shell weight and shell ratio were carried out in eight generations. Heritability and correlation coefficients were estimated by REML method. Heritability of cocoon weight and cocoon shell weight were higher than heritability of cocoon shell ratio. Genetic correlation between cocoon weight and cocoon shell weight for 107, 101433 and 153 lines were 0.921, 0.911 and 0.915, respectively. Genetic correlation between cocoon weight and cocoon shell percentage for 107, 101433 and 153 lines were -0.229, 0.374 and 0.088, respectively. Genetic correlation between cocoon shell weight and cocoon shell percentage for 107, 101433 and 153 lines were 0.699, 0.830 and 0.800, respectively. The highest heritability for cocoon weight belonged to 101433 (0.468) lines. Also the lowest heritability for cocoon weight belonged to 153 (0.400) line. The highest and lowest heritability for cocoon shell weight belonged to 101433 (0.503) and 107 (0.292) lines, respectively. Meanwhile the highest and lowest heritability for cocoon shell percentage belonged to 101433 (0.259) and 153 (0.172) lines, respectively. With respect to the results of this study it is concluded that separate breeding strategy must be designed in the varieties and different selection index constructed. Also economic characters have high heritability showing that individual index selection can be performed efficiently to improve important traits in a few generations.
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