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United States Department of Agriculture

Agricultural Research Service

Title: Shared Genetic Basis of Resistance to Bt Toxin Cry1ac in Independent Strains of Pink Bollworm

Authors
item Tabashnik, B - UNIV. AZ, TUCSON, AZ
item Liu, Yong Biao
item Morin, S - UNIV.JERUSALEM,ISRAEL
item Unnithan, Devika - UNIV. AZ, TUCSON, AZ
item Carriere, Y - UNIV. AZ, TUCSON, AZ
item Dennehy, T - UNIV. AZ, TUCSON, AZ

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 17, 2004
Publication Date: June 20, 2004
Citation: Tabashnik, B.E., Liu, Y., Morin, S., Unnithan, D., Carriere, Y., Dennehy, T.J. Shared genetic basis of resistance to bt toxin cry1ac in independent strains of pink bollworm. Journal of Economic Entomology. 2004. v. 97. p. 721-726.

Interpretive Summary: Using feeding bioassays and molecular genetic techniques, we found that two independently derived resistant pink bollworm strains shared a same locus at which three mutant alleles confer resistance to Bt toxin Cry1Ac. The two strains were previously reported to show traits of recessive resistance, the most common mode of lepidopteran resistance to Bt toxin Cry1Ac. Offspring from crosses between the two stains were resistant to Cry1Ac indicating shared resistant locus by the two strains. PCR tests showed presence of previously identified three resistance alleles in both strains. These results suggest that the same resistance to Bt toxin Cry1Ac may be widespread in pink bollworm populations. Therefore, they may be useful for monitoring resistance to Cry1Ac-producting Bt cotton in field populations of pink bollworm.

Technical Abstract: Classical and molecular genetic analyses show that two independently derived resistant strains of pink bollworm (Pectinophora gossypiella [Saunders]) shared a genetic locus at which three mutant alleles confer resistance to Bacillus thuringiensis (Bt) toxin Cry1Ac. One laboratory selected resistant strain (AZP-R) was derived from individuals collected in 1997 from 10 Arizona cotton fields, while the other (APHIS-98R) was derived from a long-term susceptible laboratory strain. Both strains were previously reported to show traits of 'mode 1' resistance, the most common type of lepidopteran resistance to Cry1A toxins. Inheritance of resistance to a diagnostic concentration of Cry1Ac (10µg per g diet) was recessive in both strains. In interstrain complementation tests for allelism, F1 progeny from crosses between the two strains were resistant to the diagnostic concentration of Cry1Ac. These results indicated that the resistance locus was shared by the two strains. Analysis of DNA from the pink bollworm cadhering gene (BtR) using allele-specific polymerase chain reaction (PCR) showed that the previously identified resistance alleles (r1, r2 and r3) occurred in both strains, but their frequencies differed between strains. In conjunction with previous findings, the results reported here suggest that PCR-based detection of the three known cadherin resistance alleles might be useful for monitoring resistance to Cry1Ac in pink bollworm.

Last Modified: 8/22/2014
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