棉铃虫对BT棉极低抗性等位基因的遗传检测

Isofemale line F2 screen procedure using Bt cotton, 33B(Cry1Ac), plants(5~7 leaf stage) and its criterion (survival larvae that had reached the mid-second instar with body weight ≥0.8mg/L after 5 days on Bt cotton were considered resistant homozygous) were established by comparing the efficacy of 4 Bt cotton specieses against Helicoverpa armigera larvae. A high level of resistance strain (resistance ratio=1680-fold) was obtained after 42 selections with Bt cotton. Reciprocal crossings (F1 and F1′) showed that the resistance to Cry1Ac protoxin and 21% MVPII WP were incompletely recessive trait (D= -0.24 ~ -0.26). Using F2 genetic method of isofemale lines to detect the frequency of resistance alleles to Bt toxin from transgenic Bt cotton, 33B, in the insect. The results showed that frequency of resistance allele in natural insect population reached to >0.58% (95%CI=0~1.88%). Compared with other methods for detecting and estimating resistance alleles, F2 screen will be efficient and accurate, extend the sensitivity of allele-frequency estimation for recessive traits by more than 1~2 order of magnitude compared with conventional resistance ratio and discriminating-dose assay and suit to the early detection of resistance. The results monitored showed that the frequency o resistance alleles to Bt cotton increased significantly as the years that transgenic Bt cotton has been planted in the cotton bollworm field population in Wei county, Hebei province where Bt cotton has been planted for 3~5 years from 2000 to 2002. So far, the frequency reached up to 9.37% (95%CI=1.93~16.86%). There is a high risk of developing resistance to transgenic Bt cotton in H. armingera. Furthermore, two critical assumptions of the preventive resistance management strategy, high-dose/ refuge, were studied. The results showed that the Bt toxin expressing from the main stems and lateral branch terminal leaves in mid- and later season were not high level, and a resistant strain of larvae on Bt cotton takes longer to develop than susceptible larvae on non-Bt cotton. The non-high-level of Bt toxin expression and developmental asynchrony could reduce the expected benefits of the refuge strategy.

转BT基因棉是分子遗传工程技术的一项重要成果,它为控制我国棉铃虫猖獗危害提供了新途?本项目通过建立BT棉高毒标准\极低抗性等位基因频率遗传检测技术\抗性基因遗传特性及生物学特性,评估和制定预防性抗性治理方案.这对促进我国转基因棉的推广应用\棉铃虫防蝄棉花的持续高产及生物技术发展具有重要的理论和现实意义..