2019 Volume 27 Pages 115-131
Recently, there are demands for silkworm races which are superior in quantitative traits, easy to rear, and characterized by cocoon thread like thick and thin filament and double cocoons. Focusing on the fact that the physical properties of raw silk are different among silkworm races, we measured the strength, elongation and Young’s modulus of the silk for the regional type of the races possessed by NARO in order to establish a new breeding basis. As a result, the average value in Chinese native races was highest in strength, the elongation was in Improved European races, and the Young’s modulus was highest in European native races. In the comparison of individual race, there were races showing the maximum value of 6 kgf/d in strength or the value of 38.5% in elongation. In order to add these superior properties to silkworm races, we made a crossbred generation (F1) between existing type and high strength type and investigated inheritance on high strength properties. F1 with a parent of high strength or thin thread race has high value in strength, and F1 with a parent of thick thread is high value in elongation. These findings indicate that there is a moderate correlation between strength extension and size of thread. In this study, based on the results, we tried crossbreeding between existing race and high-strength strain and tried creating material for new silkworm race with excellent strength.