Vol. 11, Issue 11 (2022)

Three muscardine resistant thermotolerant bivoltine breeds viz., B1, B4 and B8 were crossed with a productive but muscardine susceptible bivoltine breed CSR₄ to raise six generations viz., P1, P2, F₁, F₂, BC₁ and BC₂ which were all reared at once. A batch of silkworms of all the generations were inoculated with 9.04 × 10⁴ spores / ml of B. bassiana @ 0.5 ml per silkworm to know their performance under fungal stress and another batch was reared under normal condition. The results revealed that among the non-segregating generations of the thermotolerant bivoltine silkworms, B1 breed and F₁ of (B1 × CSR₄) performed better for cocoon parameters viz., cocoon, shell and pupal weights and pupation rate and silk parameters viz., filament length and filament weight under normal conditions. However, B4 breed and F₁ of (B4 × CSR₄) performed better for these traits under muscardine inoculation. Whereas, CSR₄ breed and F₁ of (B8 × CSR₄) performed better for denier under both normal and muscardine disease conditions. Among segregating generations, F₂ of (B1 × CSR₄), BC1 of (B1 × CSR₄) × B1 and BC2 of (B1 × CSR₄) × CSR₄ crosses performed better for the cocoon parameters studied viz., cocoon, shell and pupal weights and pupation rate and silk parameters viz., filament length and filament weight under normal conditions. While under muscardine infection, F₂ of (B4 × CSR₄), BC1 of (B4 × CSR₄) × B4 and BC2 of (B4 × CSR₄) × CSR₄ crosses performed better for these traits. Whereas, F2 of (B8 × CSR₄), BC1 of (B1 × CSR₄) × B1 and BC2 of (B8 × CSR₄) × CSR₄ crosses performed better for denier under both normal and muscardine disease conditions. Thus, it could be concluded that thermotolerant bivoltine silkworm breed B4 could be used for further improvement of the breeds for dual stress tolerance.