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Save Our Pathogens New Scientist 22 Aug 98 5

THE millions of viruses, bacteria and fungi that kill or blight plants worldwide should be conserved with the same urgency as other species, says a group of biologists. 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 7th International Congress on Plant Pathology in Edinburgh last week, they argued that saving wild flowers and trees is no longer enough. They called on governments and conservation organisations to develop plans to protect the genetic diversity of the disease microorganisms to which plants play host. Pathogens are a vital part of the evolutionary process, says David Ingram, president of the British Society for Plant Pathology and Regius Keeper of the Royal Botanic Garden in Edinburgh, who is spearheading the campaign. They help to shape the natural environment, so eliminating them could throw whole ecosystems out of balance. The World Conservation Monitoring Centre in Cambridge estimates that 34 000 species of plant-12.5 per cent of the world's flora-are facing extinction. "For every plant that becomes extinct, 30 other species go with it and many of these will be plant pathogens," says Ingram. "With the continuing rapid loss of habitats and ecosystems worldwide, the increased use of fungicides, pesticides and herbicides in agriculture and the release of genetically modified organisms, the threats to pathogen diversity in the wild are immense." Ingram told the Edinburgh conference that scientists are only aware of a tiny proportion of the world's fungi, viruses and bacteria. Understanding the natural resistance that pathogens provoke in wild plants would help in breeding food crops that can resist disease. This will be crucial for feeding the world's growing population next century, he said. Several studies presented at the meeting illustrate how pathogens can interact with plants to determine the structure of ecosystems. Everett Hansen of Oregon State University in Corvallis 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 grow. Wim van der Putten 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 the 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 (Q. petraea), but rarely kills either. Oak trees have evolved with the disease over millennia, she said. "Conservation of host and pathogen are necessary to preserve the total ecosystem. To eradicate the pathogen would lead to a series of unpredictable changes." Rob Edwards

   est. no. species  known number
 bacteria  3,000,000  4000 (0.1%)
 fungi  1,500,000  70,000 (5%)
 viruses  500,000  5000 (1%)