About 90% of India’s total cotton cultivated area is occupied by hybrid Bt-cotton to utilize hybrid vigor. Hybrids with both Cry1Ac and Cry2Ab genes were found to be susceptible to pink bollworm (PBW) attack. Research was conducted to analyze the segregating pattern of these genes in selfed bolls of different generations with PBW damage. The average number of seeds per boll containing Cry1Ac in F1 was 14.8 ± 1.303 (2022) and 13.8 ± 2.16 (2023), and Cry2Ab gene in F1 was 12.4 ± 0.894 (2022) and 17.8 ± 1.64 (2023). In F2 single-boll selfed seeds, the number of seeds was reduced compared to F1 for Cry1Ac gene, whereas for Cry2Ab, the seed number was similar to F1. In advanced breeding lines, the number of Cry1Ac-positive seeds was high compared to F1 and F2. As for the segregating pattern for Cry1Ac and Cry2Ab genes in the F2 generation, an expected ratio of 3:1 was observed for two years. The highest field incidence of PBW infection was noted for the Bt variety Rajat Bt in 2022 and 2023. Results can vary based on the zygosity of the parents used in hybrid development. Research revealed that gene segregation lowers Bt toxicity and increases PBW infestation thereby decreasing the viability of Bt plants. Another way to overcome resistance is by stacking these Cry genes in a variety rather than a hybrid. As all the genes will be in homozygous condition, the toxicity produced will be higher and uniform throughout the entire population.
