title: Genetic basis of resistance to Cry1Ac and Cry2Aa in Heliothis virescens (Lepidoptera: Noctuidae).
abstract: The development of pest resistance to transgenic crop plants producing insecticidal toxins from Bacillus thuringiensis Berliner (Bt) poses a major threat to their sustainable use in agriculture. "Pyramiding" two toxins with different modes of actions in the same plant is now being used to delay the evolution of resistance in the insects, but this strategy could fail if a single gene in a pest confers resistance to both toxins. The CP73 strain of the cotton pest Heliothis virescens (F.) is resistant to both Cry1Ac and Cry2Aa toxins from Bt. We explored the genetic basis of resistance in this strain with a backcross, split-family design. The gene with the largest effect on Cry1Ac resistance in CP73 (BtR-5) maps to linkage group 10 of H. virescens and thus differs from the previously described linkage group 9 BtR-4 resistance found in the YHD2 strain, involving mutation of the gene encoding a 12-domain cadherin-like binding target of the Cry1A toxins. Neither BtR-4 nor BtR-5 seems to confer significant resistance to Cry2Aa. A majority of the linkage groups studied in one backcross family made a small positive contribution to resistance for both toxins. Thus, the Cry2Aa resistance in CP73 is not caused by either of the two major Cry1Ac resistance-conferring genes but instead probably has a quantitative genetic basis.
authors.affiliation: Department Biological Sciences, Clemson University, Clemson, SC 29634, USA.
authors.forename: Linda J
authors.initials: LJ
authors.lastname: Gahan
authors.forename: Yun-Tao
authors.initials: YT
authors.lastname: Ma
authors.forename: Mary Lynn MacGregor
authors.initials: ML
authors.lastname: Coble
authors.forename: Fred
authors.initials: F
authors.lastname: Gould
authors.forename: William J
authors.initials: WJ
authors.lastname: Moar
authors.forename: David G
authors.initials: DG
authors.lastname: Heckel
mesh_terms: D000818:Animals; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004731:Endotoxins; D008040:Genetic Linkage; D006460:Hemolysin Proteins; D019476:Insect Proteins / Q000235:genetics; D007305:Insecticide Resistance / Q000235:genetics*; D007306:Insecticides; D007814:Larva / Q000254:growth & development; D009036:Moths / Q000235:genetics*; D009154:Mutation
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004731:Endotoxins; D006460:Hemolysin Proteins; D019476:Insect Proteins; D007306:Insecticides; C030956:insecticidal crystal protein, Bacillus Thuringiensis