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1 June 2005 Association Between Resistance to Bt Cotton and Cadherin Genotype in Pink Bollworm
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Two strains of pink bollworm, Pectinophora gossypiella (Saunders), each derived in 1997 from a different field population, were selected for resistance to Bacillus thuringiensis (Bt) toxin Cry1Ac in the laboratory. One strain (MOV97-R) originated from Mohave Valley in western Arizona; the other strain (SAF97-R) was from Safford in eastern Arizona. Relative to a susceptible laboratory strain, Cry1Ac resistance ratios were 1700 for MOV97-R and 520 for SAF97-R. For the two resistant strains, larval survival did not differ between non-Bt cotton and transgenic cotton producing Cry1Ac. In contrast, larval survival on Bt cotton was 0% for the two unselected parent strains from which the resistant strains were derived. Previously identified resistance (r) alleles of a cadherin gene (BtR) occurred in both resistant strains: r1 and r3 in MOV97-R, and r1 and r2 in SAF97-R. The frequency of individuals carrying two r alleles (rr) was 1.0 in the two resistant strains and 0.02 in each of the two unselected parent strains. Furthermore, in two hybrid strains with a mixture of susceptible (s) and r alleles at the BtR locus, all survivors on Bt cotton had two r alleles. The results show that resistance to Cry1Ac-producing Bt cotton is associated with recessive r alleles at the BtR locus in the strains of pink bollworm tested here. In conjunction with previous results from two other Bt-resistant strains of pink bollworm (APHIS-98R and AZP-R), results reported here identify the cadherin locus as the leading candidate for molecular monitoring of pink bollworm resistance to Bt cotton.

Bruce E. Tabashnik, Robert W. Biggs, Dawn M. Higginson, Scottie Henderson, Devika C. Unnithan, Gopalan C. Unnithan, Christa Ellers-Kirk, Mark S. Sisterson, Timothy J. Dennehy, Yves Carrière, and Shai Morin "Association Between Resistance to Bt Cotton and Cadherin Genotype in Pink Bollworm," Journal of Economic Entomology 98(3), 635-644, (1 June 2005).
Received: 22 December 2004; Accepted: 1 February 2005; Published: 1 June 2005

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