Molecular stacking of two codon-modified genes encoding Bt insecticidal proteins, Cry1AcF and Cry2Aa for management of resistance development in Helicoverpa armigera

Concurrent expression of multiple insecticidal toxins as pyramided genes in the same host plant is one of the tangible strategies to delay the development of resistance in insects. In this study, an ideal combination of Insecticidal Cry Proteins (ICP) of Bacillus thuringiensis ( Bt ) viz., chimeric Cry1AcF (produced by domain swapping) and Cry2Aa (a synthetic protein with modified codon usage for plants) were selected. The main aim of this study was to determine whether the combination of two cry genes can confer better protection against Helicoverpa armigera over single a cry gene. Transgenic tobacco plants harbouring single and double ICP genes were generated and analysed for their insecticidal activity against cotton bollworm ( H . armigera ) through detached leaf insect bioassay. Efficacy studies showed that transgenic plants carrying the combinatorial construct had higher insecticidal activity compared to the individual genes and required lesser time for effective and maximum mortality of the pest. Molecular analysis and protein expression analysis of transgenic tobacco plants also correlated with the bioassay results. This study suggests that transgenic tobacco plants having both the toxins can be an effective option against H. armigera . However, the toxin combination should be carefully selected depending upon the most important pest species present in each geographical area.