By IPS Correspondents
MEXICO CITY, Aug 9 2003 (IPS)

Potatoes armed with genes resistant to the crop’s leading enemy, late blight, are undergoing trial by fire in Mexico by being exposed to the disease in open field tests. So far, the potatoes have been winning, though it is only a partial victory.

Scientists from the University of Wisconsin in the United States discovered the group of RB genes responsible for the disease resistance, but they would have never been able to do it without wild Mexican potato species Solanum bulbocastanum.

In this potato, which is not grown commercially, they found the genes that make the plant impervious to Phytophthora infestans, the "oomycete pathogen" that triggers late blight, a disease that originated in Mexico and spread throughout the world in the 19th century.

Using genetic engineering techniques, the RB genes have been cloned and inserted into the cells of commercially grown potato varieties, a process described in the study published in July in the U.S.-based journal Proceedings of the National Academy of Sciences.

John Helgeson, head of the research team that made the discovery, told Tierramérica, that the interest in finding a solution to the disease emerged from the realisation that late blight was causing massive losses in potato crops in the United States, Latin America and Europe.

The potato, domesticated in the Andean regions of South America some eight thousand years ago, is today one of the world’s most important food crops, with annual yields reaching 300 million tonnes.

The main disease affecting this plant is late blight. Until recently it was believed to be caused by a type of fungus, but two years ago it was reclassified as a brown algae.

"Late blight was responsible for the European potato famine in the 19th century, which caused the starvation deaths of more than one million people in Ireland alone," states the journal article, "Gene RB cloned from Solanum bulbocastanum confers broad spectrum resistance to potato late blight."

Today, the disease is usually controlled by the application of large quantities of fungicides, most of which are harmful to the environment and a financial burden for farmers.

The RB gene could represent an alternative to the use of agrochemicals, thanks to the discovery by Helgeson and his colleagues, experts in plant pathologies. But further tests and crossbreeding must still be conducted before the benefits can be disseminated for use by farmers.

The potatoes with the new genes have been grown in Mexico since 1995 on experimental plots in Toluca Valley, near the nation’s capital. The area is home to the world’s most aggressive form of late blight.

Farmers in Toluca Valley must apply fungicides as many as 26 times a year in order to protect their commercial potato crops from the disease.

The results in the test plots there indicate that the tubers with RB genes are affected by late blight at a rate of less than 40 percent of plants cultivated. The bad news is that the potato is smaller and not attractive to the consumer.

"A great deal of testing is needed before the late blight-resistant potato reaches the point at which it will be commercially viable, and there is no guarantee that the varieties produced will be appealing to all potato consumers around the world," warns Héctor Lozoya, a researcher at Mexico’s University of Chapingo and coordinator of RB gene testing in this country.

But in a conversation with Tierramérica, Lozoya recognised that the work by Helgeson’s team for the first time opens the door to truly controlling the disease without the use of chemicals.

If that is achieved, developing countries stand to benefit enormously because they would save millions of dollars in production costs, much of which is currently spent on fungicides.

Several studies show that since the 1960s the total area planted with potato in the developing world has expanded more than any other food crop.

The war against late blight began to take shape in the United States in the 1950s. Helgeson began his research in the 1980s, using some wild varieties, including some from Mexico, obtained from the National Plant Germplasm Bank, the world’s largest collection of plant cell and tissue cultures.

But Mexican scientists were not informed of the studies in the United States involving Mexican potatoes.

"We only learned of Helgeson’s work in the 1990s, when potato crops already covered 65,000 to 70,000 hectares in Mexico. In prior decades potato cultivation was very limited," said Lozoya, who is also a member of an international cooperative programme on late blight.

Due to genetic incompatibility, the wild and crop potato cannot be sexually cross-bred, so it initially seemed impossible to transmit the wild potato’s late blight resistance to the potato that is grown for human consumption.

But the U.S. research team turned to genetic engineering techniques, allowing them to extract the RB genes from the wild Mexican potato and introduce it into the commercial varieties of this root vegetable.

Helgeson is optimistic about the applications of the discovery. "The new plants have proven resistant to everything we’ve thrown at them so far," he said.

Although he admits the new variety has lower yields, the potato is not altered in its taste, nor does it pose risks to human health, he says.

People need to know, says the scientist, that this potato does not contain a gene from a fish or some bacterium, but is an organism that has been genetically modified using genes from another potato variety.

Helgeson says he is confident that there is nothing unsafe about the potato varieties derived from the introduction of RB genes, but, as in all scientific research, "many tests are needed."

Transnational agro-chemical and seed corporations that are already involved in transgenic crops, like Monsanto, have expressed interest in the RB genes.

Tierramérica learned that the transnational agro-business giant is closely watching the Helgeson team’s efforts, but with the idea of applying the knowledge to tomatoes, which also suffer late blight.

* Originally published Aug. 2 by Latin American newspapers that are part of the Tierramérica network. Tierramérica is a specialised news service produced by IPS with the backing of the United Nations Development Programme and the United Nations Environment Programme: www.tierramerica.net

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