Evolution of resistance by pests is the main threat to long-term insect control by transgenic crops that produce Bacillus thuringiensis (Bt) toxins. We previously identified three mutant alleles (r1, r2, r3) of a cadherin gene in pink bollworm (Pectinophora gossypiella) linked with recessive resistance to Bt toxin Cry1Ac and survival on transgenic Bt cotton. Here we describe a polymerase chain reaction (PCR)-based method that detects the mutation in genomic DNA of each of the three resistant alleles. Using primers that distinguish between resistant and susceptible (s) alleles, this method enables identification of 10 genotypes (r1r1, r1r2, r1r3, r2r2, r2r3, r3r3, r1s, r2s, r3s, and ss) at the cadherin locus. For each of the three resistant alleles, the method detected the resistance allele in a single heterozygote (r1s, r2s, or r3s) pooled with DNA from the equivalent of 19 susceptible (ss) individuals. The results suggest that the DNA-based detection method described here could greatly increase the efficiency of monitoring for resistance to Cry1Ac compared to bioassays that detect rare individuals with homozygous resistance.
Bibliographical noteFunding Information:
We thank R. Biggs, D. Unnithan, and the staff of the Extension Arthropod Resistance Management Laboratory for technical assistance. Xianchun Li, Dawn Higginson and Iris Karunker provided helpful comments on the manuscript. This work was supported by Vaadia-BARD Postdoctoral Fellowship FI-300-2000, the University of Arizona, Cotton Incorporated, the Arizona Cotton Research & Protection Council, Monsanto, the Cotton Foundation, USDA-NRI grants 99-35302-8300, 2001-35302-09976 and 2003-01649, and USDA Biotechnology Risk Assessment Grants 2001-33120-11213 and 2003-04371. S. Henderson was funded by the Center for Insect Science through NIH training grant 1K12GM00708.
- Bacillus thuringiensis
- Bt cotton
- Molecular monitoring
- Pectinophora gossypiella
- Resistance detection