Can GM crops end food supply shortage fears?

Worldwide, some 90m hectares of GM crops are cultivated each year and 68% of soybeans and 40% of corn (maize) production is now GM. The technology is also making dramatic advances.

Traits for herbicide resistance (mainly glyphosate or glufosinate) and insect resistance (Bt) have been added to crops for some years but increasingly genes are being "stacked" into the same variety eg. glyphosate resistance + resistance to insect pests. Recently in the USA, Dow AgroSciences and Monsanto announced they had developed a corn variety incorporating eight different herbicide tolerance and insect resistance genes.

America is undoubtedly leading the way with some 55m ha of GM crops grown annually (compared with less than 0.1m hectares in the EU). Nowhere is it more evident than in the Midwestern state of Iowa (see box).

Predicted bioethanol growth means that in this state alone, corn production will have to increase by 160% to meet the food and fuel demand. Mike Owen from Iowa State University believed GM technology would be crucial to doing this in an environmentally sustainable way.

"Perhaps one of the most important successes has been the savings, environmental and economic, resulting from the change to conservation tillage - particularly no tillage - attributable to GM crops."

Soil erosion, sedimentation of watercourses and diesel use had all been cut as a result, he said. In addition, growers had achieved more consistent weed control, and there was a perceived yield advantage.

In Minnesota, the use of Bt corn had dramatically cut the damage caused by European Corn Borer - a pest which caused annual losses of $1bn across the USA, the University of Minnesota's Bill Hutchison added. Around half of all corn grown there has the gene and average pest numbers had fallen to around 29 per 100 plants, compared with 82 per 100 plants historically.

"It's still unclear how these new genes coming on to the market will affect things."

Problems emerging

Aside from any moral or ethical issues, problems with the adoption of GM crops are becoming more apparent as their uptake increases. There was evidence of evolved pesticide resistance in some weed species and pest pressures were also shifting, Prof Owen said. "New pests are coming in, such as the western beet cutworm."

Pollen transfer meant there had also been introgression of GM traits into non-GM crops, such as maize and canola, making volunteers harder to control.

New weed pressures were also emerging, such as Commelina communis (Asiatic dayflower), which had never been seen until the introduction of herbicide-tolerant soybeans.

Many of the problems were a result of poor understanding of basic ecological principles, especially selection pressure, and "major misconceptions" about the simplicity of GM crops, he said. "A lot of the changes are happening at an increasing rate, because of the intense selection pressure imposed."

There is also significant concern that growers are not adhering to legal stewardship rules for growing GM crops. For example, growers were required to plant refuge (non-GM) crops (totalling 20% of area), but many were not doing so - on the assumption their neighbours would, he said.

"There's no question of the value of GM crops we see on-farm from an environmental, food quality and economic point of view. However, we can't ignore the issues."