February 7, 2003

from Nature Science Update
by John Whitfield

In India, genetically modified (GM) cotton produces crops that are 80% larger than conventional varieties, farm trials from 2001 have found.

Results from last year's commercial harvest were similar, although less spectacular, says the Indian biotech industry. But environmental groups dispute this.

GM crops will be especially useful in tropical developing countries, says agricultural economist Matin Qaim of the University of Bonn in Germany. "Population growth and limited farmland mean that we need yield advantages," he says. Qaim and his colleague David Zilberman looked at 157 typical cotton farms in three Indian states¹.

Farmers grew Bt transgenic cotton alongside two non-GM varieties. Bt plants carry a gene for a toxin from bacteria that makes them resistant to bollworm caterpillars. Indian cotton farmers typically lose about half of their crop to pests.

Bt cotton gave 80% higher yields, and used almost 70% less pesticide, than conventional varieties. The GM seed costs four times as much as normal cotton, but the yield improvements mean that the crop is worth five times as much, says Qaim.

The benefits of Bt cotton in 2001 were unusually large, as bollworm populations were high. Over several years, the farm trials show that Bt cotton yields about 60% more than conventional varieties. "Farmers were very positive," says Qaim. "There were not enough seeds available to satisfy demand."

Trials in South Africa have shown similar results and met with a similar reaction, says development researcher Stephen Morse of the University of Reading, UK: "I concur completely with what Qaim is saying."

The benefits seen for cotton may not extend to other crops, says Morse. Species such as maize are affected more by soil quality and water than pests. Maize also has a wider range of pest species, which the Bt gene would not protect against.

Seed money

Others deny that Bt cotton is better. "I have personally conducted a study in two states, and have found a drastic failure of transgenic Bt cotton," says Afsar Jafri, deputy director of the Research Foundation for Science, Technology and Ecology, a New Delhi-based conservation group. The foundation says that Bt cotton has shown worse yields and more pests than conventional varieties.

Bt cotton has a controversial history in India. Farmers have burnt crop trials, and illegally grown GM plants have been found. GM cotton was grown commercially in India for the first time in 2002.

About 40,000 of the 90 million hectares of Indian cotton in 2002 were Bt varieties. These GM crops yielded 30% more than conventional varieties, increasing farmers' incomes by about 3,000 rupees (US$63) per hectare, says Ranjana Smetacek of Mahyco-Monsanto Biotech, the Mumbai-based company that sells Bt seed in India. Smetacek expects that there will be more than 250,000 hectares of Bt cotton in 2003.

In temperate regions such as North America and China, Bt cotton yields little more than conventional varieties. "A 2-3% improvement is fairly typical in the United States," says cotton researcher Fred Bourland of the University of Arkansas in Keiser. In the tropics there is more room for improvement: pests do more damage, farmers have less access to pesticides, and pesticide resistance is more common.

Worm turns

There was another thumbs-up for Bt cotton this week. US researchers announced that in Arizona over the past decade the spread of resistant cotton has led to a drop in the bollworm population². The finding suggests that planting areas of non-GM cotton is working to prevent pests evolving resistance to the Bt variety.

1. Qaim, M. & Zilberman, D. Yield effects of genetically modified crops in developing countries. Science, 299, 900 - 902, (2003).
2. Carrière, Y. et al. Long-term regional suppression of pink bollworm by Bacillus thuringiensis cotton. Proceeding of the National Academy of Sciences, published online, doi:10.1073/pnas.0436708100 (2003).

The article can be found in Nature magazine.

© Nature News Service / Macmillan Magazines Ltd 2003