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Applied and Environmental Microbiology, September 2000, p. 3784-3789, Vol. 66, No. 9
Department of Entomology, Cornell University,
New York State Agricultural Experiment Station, Geneva, New York
144561; Department of Plant Breeding,
Cornell University, Ithaca, New York 148532;
Department of Crop Protection, Waite Institute, South Australia
5064, Australia3; and Department of
Genetics, University of Valencia, 46100-Burjassot (Valencia),
Spain4
Received 20 March 2000/Accepted 15 June 2000
A field-collected colony of the diamondback moth, Plutella
xylostella, had 31-fold resistance to Cry1C protoxin of
Bacillus thuringiensis. After 24 generations of selection
with Cry1C protoxin and transgenic broccoli expressing a Cry1C protein,
the resistance that developed was high enough that neonates of the
resistant strain could complete their entire life cycle on transgenic
broccoli expressing high levels of Cry1C. After 26 generations of
selection, the resistance ratios of this strain to Cry1C protoxin were
12,400- and 63,100-fold, respectively, for the neonates and second
instars by a leaf dip assay. The resistance remained stable until
generation 38 (G38) under continuous selection but decreased to
235-fold at G38 when selection ceased at G28. The Cry1C resistance in
this strain was seen to be inherited as an autosomal and incompletely recessive factor or factors when evaluated using a leaf dip assay and
recessive when evaluated using Cry1C transgenic broccoli. Saturable
binding of 125I-Cry1C was found with brush border membrane
vesicles (BBMV) from both susceptible and Cry1C-resistant strains.
Significant differences in Cry1C binding to BBMV from the two strains
were detected. BBMV from the resistant strain had about sevenfold-lower
affinity for Cry1C and threefold-higher binding site concentration than
BBMV from the susceptible strain. The overall Cry1C binding affinity was just 2.5-fold higher for BBMV from the susceptible strain than it
was for BBMV from the resistant strain. These results suggest that
reduced binding is not the major mechanism of resistance to Cry1C.
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Development and Characterization of Diamondback
Moth Resistance to Transgenic Broccoli Expressing High Levels
of Cry1C

*
Corresponding author. Mailing address: Department of
Entomology, Cornell University, New York State Agricultural Experiment Station, Geneva, NY 14456. Phone: (315) 787-2352. Fax: (315) 787-2326. E-mail: ams5{at}cornell.edu.
Present address: Department of Entomology and Plant Pathology,
Mississippi State University, Mississippi State, MS 39762.
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