ABSTRACT
Herbicide-resistant crops (HRCs) will find grower acceptance if there are no detrimental effect of the resistance genes on plant growth, quality, and/or yield of the crop. This chapter deals with crops that have been modified for resistance to specific herbicides. Pleiotropy is the phenomenon whereby a change at one genetic locus can bring about a variety of apparently unconnected phenotypic changes. Triazine-resistant canola was produced by crossing a naturally occurring triazine-resistant B. campestris with B. napus. Triazine-resistant canola is an example of the acceptance of decreased yield in exchange for weed control. Acetolactate synthase (ALS) is the first common enzyme in the biosynthetic pathways of the branched chain amino acids, leucine, valine, and isoleucine. Sulfonylurea-resistant tobacco was produced through transformation using a sulfonylurea-resistant mutant ALS gene from Arabidopsis. Glyphosate-resistant crops have been produced through overproduction of the 5-enolpyruvylshikimate 3-phosphate (EPSP) synthase, by incorporating a less sensitive 5-enolpyruvylshikimic acid-3-phosphate synthase (EPSP synthase), and by introducing a gene that degrades glyphosate.
