PERHAPS it鈥檚 because they take an age to grow and then fade into the landscape. Or it could simply be that we don鈥檛 eat them. Whatever the reason, genetically modified trees have never raised such fierce passions as GM food crops.
But this week, for the first time, a team of geneticists has tried to evaluate the risks posed by GM trees to native woods and forests. Critics of biotech have applauded the move, saying that, for once, we may actually have some evidence on the risks of GM plants before the debate begins in earnest.
GM trees are being developed for a variety of uses, though none is yet grown on a commercial scale. The good news is that if they were, they would only rarely cross-breed with wild relatives 鈥� and then only with nearby trees.
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Steven Strauss from Oregon State University in Corvallis and his team evaluated the spread of pollen between commercial plantations of conventionally bred hybrid poplars and wild black cottonwood poplars growing nearby. As markers, they identified stretches of DNA unique to pollen from the commercial poplars, then screened for these markers in tissue and seeds from wild trees.
A thorough search by Strauss鈥檚 team revealed that the plantation trees cross-pollinated only with wild relatives growing just over the boundary fence. Even then, only between 0.1 per cent and 1 per cent of these neighbouring wild cottonwood trees were affected, far fewer than the team expected.
Strauss and his colleague Stephen DiFazio from Oak Ridge National Laboratory in Tennessee warn that pollen from GM trees still has the potential to spread novel genes far and wide. Trees produce copious pollen and it travels up to 16 kilometres, eight times as far as pollen from oilseed rape (canola), the most promiscuous GM crop. 鈥淕enes will get out into the environment. It鈥檚 simply a matter of degree, and whether they have any harmful effects,鈥� says Strauss, who presented the team鈥檚 results in Amsterdam this week to a conference on gene flow.
Sue Mayer of the British pressure group GeneWatch welcomes the research. 鈥淚 think it鈥檚 really good that someone is trying to get some baseline information from conventional trees,鈥� she says. 鈥淚t was precisely this data we lacked to inform the debate on GM crops such as oilseed rape.鈥�
Some of the GM trees now being developed are resistant to weedkillers or pests. Others have soft wood that can be pulped with milder chemicals than normal timber.
Strauss and his team are now plugging the data into a computer program that will predict the environmental impact of GM poplars over decades. His hunch is that only those GM traits that confer some fitness advantage, such as pest resistance, will have a significant impact. But he suggests that growers play safe by creating sterile trees that cannot cross-pollinate.