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GM potatoes deter one pest but attract another

10:05 01 June 02
Exclusive from New Scientist Print Edition
An attempt to make potato plants resistant to sap-sucking insects has highlighted the unpredictability of genetic engineering. The modified plants unexpectedly turned out to be vulnerable to other kinds of insect pests, demonstrating how important it is to assess each transgenic crop individually.
Repel the aphids and you attract the leafhoppers (Photo: Stone)
Crops such as maize and cotton have already been made resistant to chewing insects by adding a gene for the bacterial toxin Bt. But Bt does not deter sap-suckers like aphids, so genetic engineers are looking at other natural substances to keep insects at bay, such as the lectin proteins found in many plants and seeds.
Lectins have a controversial history. It was lectin-transformed potatoes created by Arpad Pusztai that set off a storm in Britain about the safety of GM food. Now Nick Birch's team at the Scottish Crop Research Institute near Dundee has found that potato plants transformed with lectin genes have lower levels of bitter-tasting chemicals called glycoalkaloids that make plants unpalatable to many mammals and insects.
Glycoalkaloid levels in the leaves of the lectin-transformed potatoes dropped by up to 44 per cent. This seems to be due to the genetic engineering technique itself, because introducing another type of gene, for another potential insect deterrent called cowpea trypsin inhibitor, also caused glycoalkaloid levels in the plants to drop by 70 per cent.
The team warns that plants with lower glycoalkaloid levels could be more vulnerable to a range of insect pests, including the potato leafhopper. And reduced levels of the glycoalkaloid alpha-chaconine actually stimulates the potato aphid to feed.

Cracked stems

The results are surprising, says Angelika Hilbeck, an ecologist at the Swiss Federal Institute of Technology in Zurich who studies the risks posed by GM crops. "We need to learn a lot more about the unintended side effects of the various transformation techniques."
While the potatoes were only experimental varieties, unexpected side effects have also turned up in commercial GM crops. The stems of a herbicide-resistant soya bean created by Monsanto were found to crack open in hot climates, for instance (New Scientist, 20 November 1999, p 25).
Unintended effects also occur in traditional breeding programmes, points out Howard Davies of the Scottish Crop Research Institute. But he says new techniques should help us to get a grip on the problem.
"Technologies are now being developed to measure several hundreds, if not thousands, of metabolites in plants using metabolic profiling procedures," he says. These approaches, along with techniques that can profile thousands of genes or proteins simultaneously, should help reveal any possible unintended effects caused by genetic transformation, he says.
Journal reference: Annals of Applied Biology (vol 140, p 143)

Peter McGrath

Warming speeds ice sheet flow in weeks

10:47 07 June 02 news service
Hotter summer temperatures in Greenland can speed up the seaward flow of the islands massive ice-sheet in just weeks, new research shows. Previously, scientists believed that temperature changes at the surface of an ice sheet would take hundreds, if not thousands of years to affect the bottom of the sheet and speed up the flow of ice.
But now researchers have found that the Greenland ice-sheet slides faster during the summer immediately after a rise in surface melting. As soon as the melting stops at the end of the summer, the ice-sheet slows back down.
Meltwater stream flowing into a large moulin in the Greenland ice sheet (Credit: Roger Braithwaite, University of Manchester)
The rapid response could be caused by meltwater at the surface running directly to the base of the glacier through crevasses and tunnels known as moulins. The water lubricates the contact between ice and bedrock, allowing the sheet to slide faster toward the ocean.
This process has been known to boost the speed of alpine glaciers, but has not been considered for large ice-sheets before, says lead author of the study, Jay Zwally of NASA Goddard Space Flight Center in Greenbelt, Maryland.
"It's something that's never been seen before," says geophysicist Shawn Marshall of the University of Calgary in Alberta, Canada. Scientists have been sceptical about whether water could get to the base of the 1.2 km-thick ice-sheet, says Marshall. "This is pretty convincing."

Global warming

The team also found that the hotter the summer, the faster the ice flows. Using GPS measurements, Zwally and his colleagues found that during the low-melt summer of 1996, the ice-sheet sped up by 1.5 cm a day compared to winter rates. But the hotter, high-melt summers of 1998 and 1999 saw increases of 8.8 and 7.3 cm a day respectively.
Over the past two decades, summertime temperatures in Greenland have risen by about 0.25 °C. Furthermore, the portion of the ice-sheet surface that experiences melting in the summer has increased by nearly 20 per cent during that time. "Just how this may translate into increases in sea level is something we need additional research on," says Zwally.
With increased temperatures, the ice-sheet is expected to thin more rapidly at the edges. But it will also get more snow helping it to grow faster at the centre. "We don't know how much precipitation has been changing," he says.
To answer this question, NASA plans to launch a satellite in December 2002 called ICESat. It will precisely measure the elevation changes on the ice-sheet with laser altimetry to determine how snow accumulation is changing. These measurements will help reveal whether the ice-sheet is shrinking overall and how much that might contribute to sea level rise.
Journal reference: Science (DOI: 10.1126/science.1072708)

Betsy Mason

20-year study backs organic farming

19:00 30 May 02 news service
The world's longest running experiment in comparing organic and conventional farming side-by-side has pronounced chemical-free farming a success.
"We have shown that organic farming is efficient, saves energy, maintains biodiversity and keeps soils healthy for future generations," says Paul Mader of the Research Institute of Organic Agriculture in Frick, Switzerland, which carried out the 21-year study.
Although crop yields on organic plots in the experiment were on average 20 per cent lower than those on conventional plots, the ecological and efficiency gains more than made up for it, Mader says.
Soils nourished with manure were more fertile and produced more crops for a given input of nitrogen or other fertiliser. "The input of nutrients like nitrogen were as much as 50 per cent lower, so overall the organic system was more efficient," he told New Scientist.
Not all crops did equally well. Potato yields on organic plots were only 60 per cent of those on conventional plots. But organic winter wheat achieved 90 per cent, and grasses fed on manure did just as well as those fed on fertiliser.
Mader argues that the biggest bonus is the improved quality of the soil under organic cultivation, which should ensure good crops for decades to come.

Earthworms and fungi

Organic soils had up to three times as many earthworms, twice as many insects and 40 per cent more mycorrhizal fungi colonising plant roots. Soils microbes went into overdrive, transforming organic material into new plant biomass faster than microbes in conventional plots.
More predictably perhaps, organic plots contained up to 10 times as many weed species as conventional plots sprayed with herbicides.
"Under European conditions, we can clearly grow our food with much less chemical input than we do now," says Mader. "But of course a 20 per cent yield reduction in a country like India would have fatal consequences."
However, in practice, where poor farmers cannot afford expensive agrochemicals, switching to organic methods boost yields, he says: "Last year I visited a project in India, the Maikaal Project near Indore, where more than a thousand farmers are growing food organically - and increasing their yields compared to neighbouring conventional farmers."
Jules Pretty, director of the Centre for Environment and Society at the University of Essex, who recently completed a global study of organic farming, said the findings confirmed his conclusion that "organic farming is more efficient and in many circumstances can increase yields for farmers".
Journal reference: Science (vol 296, p 1694)

Fred Pearce