Herbicide tolerance: the dominant trait
Herbicide-tolerant crops (Roundup Ready soy, corn, canola) can survive applications of glyphosate herbicide that kill competing weeds. The engineered plants express an enzyme that breaks down the herbicide, allowing broad-acre weed control without crop damage.
This trait simplified weed management and reduced the need for mechanical tillage. However, heavy reliance on glyphosate selected for resistant weeds, requiring rotating herbicides or combining traits. Newer stacked traits now include tolerance to multiple herbicide classes (glufosinate, dicamba, 2,4-D).
Insect resistance and the Bt protein
Bacillus thuringiensis (Bt) is a soil bacterium producing a protein toxic to specific insect larvae but harmless to humans and non-target organisms. Corn and cotton engineered with Bt genes express this protein in every cell, killing pests like the European corn borer and cotton bollworm.
Bt crops reduced insecticide spraying dramatically on corn and cotton in the 1990s-2000s. Some regions have since seen resistance evolution in target pests, prompting resistance-management strategies like refuge areas (non-Bt crop strips allowing susceptible pest survival).
Secondary traits and emerging applications
Drought-tolerant traits (abscisic acid regulation, deeper root architecture) help crops handle water stress. Biofortified crops add micronutrients (Golden Rice with beta-carotene, vitamin-enriched cassava) for nutrition security in developing regions.
Stacked traits (combining herbicide tolerance and insect resistance in one plant) allow flexible pest management but require careful monitoring to delay resistance evolution and maintain effectiveness across generations.