Second-generation GM crops

About 29 countries grow GM crops, mainly soybean, maize, cotton and canola. The first generation of GM crops was made to control weeds and pests. The second generation adds stress tolerance, better nutrition, and genes taken from completely unrelated organisms.

Herbicide tolerance. The weedkiller glyphosate (sold as Roundup) kills plants by blocking an enzyme they need. Roundup Ready crops (canola, soybean, corn, cotton) carry a resistant form of this enzyme, from a gene of Agrobacterium. So the farmer can spray glyphosate to kill the weeds without harming the crop.

Disease resistance.

• Viral coat-protein genes put into a plant act like a vaccine, protecting it from that virus: in squash, potato, and papaya (against papaya ringspot virus).
• Genes for natural antimicrobial proteins: a defensin from alfalfa in potato (against the fungus Verticillium); a late-blight resistance gene from a wild potato relative; oxalate oxidase in chestnut; chitinase (which digests fungal walls) in apple; lysozyme genes in potato against bacterial soft rot.

Insect resistance. Bt Cry proteins (delta-endotoxins) bind to the insect gut and kill the insect. Bt cotton is India's only commercially grown GM crop (since 2002); Bangladesh was the first to plant Bt brinjal (2014). Genes can be stacked (pyramided) in one plant, for example against the fall armyworm, or combined with a drought tolerance gene (cspB). Nematode resistance is bred with the help of genetic markers.

Stress tolerance and nutrition.

• Plants that make mannitol tolerate salt; the sunflower gene HaHB4 gives drought-tolerant soybean and wheat.
• High-starch potato; non-browning apple; high-oleic (healthier oil) soybean; long-life tomato.
• Golden Rice, enriched with beta-carotene, which the body turns into vitamin A.