The Studies Of The Resistance Larvae Criterion To Bt Cotton In Cotton Bollworm Helicoverpa Armigera (HüBNER) And F1 Detection Method Of Isofemale Line

Using a Bt cotton leaf-feeding method, selection and maintenance of cotton bollworm resistance strain (YCR) were conducted. YCR was selected from 61st to 72nd generation. Resistance ratio of YCR was measured with diet infection method. The results showed that, resistant ratio of YCR to 21% MVP II WP (only containing Cry1Ac active component) was stable -2000-fold during 12episodes of selection with Bt cotton. Levels of resistance was maintained and enhanced. It would provide a guarantee for the research work about molecular mechanism of cotton bollworm resistance to transgenic Bt cotton.Using a Bt cotton leaf-feeding and toxin-impregnated Cry1Ac 18.75μg/ml diet method, the resistance criterion of cotton bollworm to transgenic Bt cotton was established through experiment of reisistant, susceptible parent and reciprocal cross. After 5 days, the results showed that, survival larvae of F1 and F1' developed to 1st~ initial-2nd instar and weighted 0.1mg~0.7mg/larvae. There were only two survival larvae of HZS that developed to 1st instar and weighted 0.1 mg. The 80.9% of surviving larvae of YCR developed to mid-2nd ~ 3rd instar and weighted≥0.8mg/larvae. The bioassay was carried out for five days with toxin-impregnated Cry1Ac 18.75μg/mL diet. The results showed that F1, F1', and HZS developed to 1st~ initial-2nd instar and weighted 0.1~0.5mg. 80% of surviving larvae of YCR developed to mid-2nd~3rd instar and weighted≥0.8mgAarvae in treated total number (50 larvae). The mean mortality of YCR, F1, F1' and HZS were, respectively, (8.0±13.0)%, (66.0±11.4)%, (66.0 ±20.7)% and (88.0±10.6)%, which of YCR was significantly different to which of F1, F1' and HZS (P<0.01). Resistance larvae criterion of cotton bollworm to transgenic Bt cotton was that developmental stage and weight of survival larvae were mid-2nd instar and ≥ 0.8mg/larvae, respectively. The results were verified by backcross inheritance experiment.On the basis of resistant strain selected by Bt cotton, Applying isofemale lines F1 method detected the resistance alleles frequency of cotton bollworm to transgenic Bt cottonin Qiu County, Hebei Province, in 2004. The results showed that, there were survival larvae developed the resistance criterion (developmental stage mid-2nd instar and weight ≥ 0.8mg/larvae ) in 32 isofemale lines with detecting 131 isofemale lines. The E(q) and Var(q) of resistance alleles in field cotton bollworm resistance to transgenic Bt cotton were respectively 12.4 × 10-2 and 4.46 × 10-4,95% confidence interval was 0.1526-0.0954.Using the PASA (PCR amplification of specific alleles) method, the results showed that 9 isofemale lines were positive in 32 isofemale lines of F1 method. The E(q) and Var(q) of resistance alleles of cDNA lesion in cadherins in field cotton bollworm resistance to transgenic Bt cotton were respectively 3.76×10-2 and 2.70× 10-4, 95% confidence interval was 0.0054-0.0698.