Inheritance of resistance to Bacillus thuringiensis toxin, Cry1Ac in Helicoverpa armigera (Hübner)

The mode of inheritance of resistance to Cry1Ac in Helicoverpa armigera through feeding bioassay on semi synthetic diet was studied. The analysis of the response of resistant, susceptible, F₁ hybrid backcross progeny and reciprocal hybrid was observed. The resistant strain DNDT-R (LC₅₀ value 6.94 μg/g) showed 231.33 fold higher resistances with respect to the susceptible strain M4-S (LC₅₀ value 0.03 μg/g). The inheritance of Cry1Ac resistance was autosomal and was inherited as a semi dominant trait. The reciprocal genetic crosses between the resistant strain DNDT-R and the susceptible strain M4-S showed dominance value (h) between 0.58 and 0.68 when calculated based on LC₅₀ value. However, the dominance of resistance depended on the Cry1Ac concentration when calculated separately for different concentrations by single concentration method. The inheritance was increasingly dominant as the concentration decreased.