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Pest Resistance
Bacillus thuringiensis (Bt) has been used by organic farmers for several
decades. Bt applications does have
several disadvantages, including cost and deactivation by sunlight and
rain. In addition, BT needs to be on
the crop when the pests are feeding, and repeated applications are
needed. Genetically modifying crops
to express Bt can overcome the problems (Mackey and Santerre,
2000).
Bt has been the most
widely used insect resistance gene (Jung, 2000). About 8.9 million hectares of Bt crops
were grown in 1999 (Pretty, 2001).
The gene encodes for the δ-endotoxin,
and this endotoxin is fatal to many insect
species’ larvae. The toxin causes cell
lysis and death, by binding to specific receptors
in the larvae gut. The δ-endotoxins are specific to lepidoptera
larvae and do not do harm to other insect species. Larvae that feed on crops expressing Bt
die instantly. There are more than
100 δ-endotoxins known, and they share between 20-90% homologous
sequences (Jung, 2000).
The use of lectins has been discussed for conferring insect
resistance (Jung, 2000). Lectins are proteins that bind to sugars and cause
cells to clump together (agglutinate) (IUPAC, 1981). However, lectins
are extremely harmful to mammals, and thus no transgenic plants have even
been field tested (Jung, 2000).
Also, α-amylase
inhibitor genes have been suggested to confer insect resistance. The polypeptides from these genes cause
staggered larvae growth by interfering with starch digestion. No commercial products have been released
(Jung, 2000).
α-amylase
protein from the yellow meal worm. Permission Pending from Glockshuber Lab.
Herbicide
Resistance
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Questions
or comments can be directed to nihesson@davidson.edu
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Page maintained by
Matt Talbert, Nicole Hesson, and Sarah Parker
Last modified April
2004
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