ABSTRACT
Cotton has been one of the most important cash crops in Pakistan, but its production is adversely affected by biotic and abiotic stresses. Insect pests such as pink bollworm present a colossal vulnerability to such a financially important commodity. Bt toxins have been widely used to safeguard agricultural plants against notorious insect pests such as cotton bollworm and pink bollworm, and they have proven to be effective in reducing chewing insect pests. However, its efficacy has been challenged due to the development of resistance in insect pests against Bt toxins such as Cry1Ac and this poses a significant risk to the long-term adoption of these Bt crops. Resistance in insect pests against Bt toxin Cry1Ac is developed due to the mutations in the midgut receptors such as cadherin. In this study first 56 amino acids which also includes helix alpha-1 portion from N-terminus of the Cry1Ac were removed and the gene was commercially synthesized following codon optimization. Modified Cry1Ac was used to develop transgenic plants of Nicotiana tabacum and insect bioassays were conducted to check the efficacy of Cry1Ac through leaf bioassays. Cry1Ac, a modified Bt toxin, was produced pET-28a (+), and diet bioassays were performed using purified protein at various doses against Pectinophora gossypiella. Based on the insect mortality and LC50, the Cry1AcM3 form of the modified toxins was shown to be more potent than the other modified versions (Cry1AcM1, Cry1AcM2), with more than 80 % mortality against resistant pink bollworm at 1.25 g/mL and an LC50 of 0.48. The results suggest that modified toxin cry1Ac may be useful in controlling population of pink bollworm resistant against cry1Ac.
