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Save the killers

THEY may be bad, but they are worth saving too. That is the message from a team of British biologists who say the millions of viruses, bacteria and fungi that kill or blight plant life across the planet should be conserved with the same urgency as other species.

Though harmful for affected plants, some plant diseases are often beneficial to ecosystems. Alarmed that many are being eradicated, the scientists have launched a campaign to "preserve the pathogen". At the seventh International Congress on Plant Pathology held a few months back in Edinburgh, UK, the biologists requested governments and conservation organisations to develop plans for protecting the genetic diversity of the disease microorganisms.

Pathogens are crucial to the evolutionary process, says David Ingram, president of the British Society for Plant Pathology and Regius Keeper of Edinburgh's Royal Botanic Garden.They help shape the natural environment, and eliminating them completely could throw whole ecosystems off balance. The World Conservation Monitoring Centre in Cambridge estimates that some 34,000 species of plant 12.5 per cent of the world's flora - are facing extinction today. "For every plant that becomes extinct, 30 other species go with it, many of which are plant pathogens," says Ingram.

Ingram told the conference that only a tiny proportion of the world's fungi, viruses and bacteria are known to scientists. Understanding the natural resistance that pathogens provoke in wild plants would help in breeding disease-resistant food crops.

Everett Hansen of Oregon State University in Corvallis, USA, showed how laminated root rot (Phellinus weirii) could improve the diversity of forests in western North America by selectively killing off certain species of pine, leaving gaps where other plants can flourish. Wim van der Puffen from the Netherlands Institute of Ecology in Heteren presented evidence at the meeting that fungi and nematodes determine the pattern of marram grass on sand dunes. And a study by researchers at Umea University in Sweden demonstrated that voles prefer to eat the herb chickweed wintergreen (Trientalis europaea) when it is infected with a smut fungus (Urocystis trientalis).

Avice Hall from UK-based University of Hertfordshire pointed out that powdery mildew (Microsphaera alphitoides) tends to damage the young leaves of one species of oak (Quercus robur) more than another species (Quercus petraea), but rarely kills either. Oak trees have evolved with the disease for over a million years now, she said. "Conservation of host and pathogen are important to preserve the total ecosystem. To eradicate the pathogen would lead to a series of unpredictable changes."

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