[Investigation of different dosages of inserted Bt genes and their insect-resistance in transgenic Bt cotton].

The plants with various dosages of inserted Bt genes were developed by intercrossing among transgenic Bt lines in which Bt genes were inserted in different chromosomes, and commercial non-transgenic Bt varieties. Laboratory bioassay of insect-resistance and Bt toxin protein assays with ELISA were used to detect efficacy to bollworm in different cotton growing stages. As transgenic Bt insect-resistant cotton, temporal difference of resistance existed in plants converging on different dosages of inserted Bt genes, i.e., there was a declining level of efficacy with plant age as the mortality (%) of Helicoverpa and Bt toxin protein expressional level decreased gradually, when analyzed with leaves from the main stem. Our research also revealed that the insect-resistance of converging 4 Bt genes plants was decreased due to homozygous suppression.