GENETICS OF WHITE MUSCARDINE DISEASE RESISTANCE IN THERMOTOLERANT BIVOLTINE SILKWORMS (Bombyx mori L.)
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Date
2022-12-18
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University of Agricultural Sciences, Bangalore
Abstract
Three thermotolerant bivoltine silkworm breeds viz., B1, B4 and B8 were crossed with CSR4 to study the genetics of white muscardine disease resistance using six generation mean analysis and disease scoring using mean, geometric and hormonic productivity. The fifth instar silkworms were topically inoculated with muscardine fungus (9.04 × 104 spores / ml @ 0.5 ml per silkworm) and assessed. Cocoon, shell, pupal and filament weights showed high heritability (h2) and high genetic advance (GA)
and larval duration, cocoon yield by weight, shell ratio, pupation rate and filament length showed high h2 and low GA both under normal condition and muscardine inoculation. Six generation mean analysis for the five quantitative traits viz., larval, cocoon, pupal and shell weights and shell ratio, revealed inadequacy of additive-dominance model indicating epistatic digenic interactions both under normal condition and muscardine inoculation. Duplicate-type epistasis played a greater role than complementary epistasis for all the five traits under normal condition. Under muscardine inoculation
complementary epistatic gene action was observed for larval, cocoon and pupal weights. The magnitude of additive gene effects [d], additive genetic variance (σ2A), dominance gene effects [h] and dominance genetic variance (σ2D) under muscardine inoculation indicated significant epistatic gene action in controlling these traits. The disease scoring for B. bassiana infection revealed that B1 × CSR4 and B4 × CSR4 hybrids showed high resistance in terms of larval and shell weights and resistance in terms of cocoon weight and shell ratio implying they being resistant hybrids and among the parents, B1 and B4
showed resistance in terms of larval and shell weights and shell ratio while moderate resistance in terms of cocoon and pupal weights. Thus, B1 and B4 can be considered as muscardine disease resistant thermotolerant bivoltine silkworm breeds. Further, the genetic parameters revealed that, hybridization and selection in later generations may yield desired results to improve muscardine disease resistant in these breeds.