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Biodiversity and Plant Pathogens and Conservation

With the publication by the World Conservation Monitoring Centre of the first IUCN Red List of Threatened Plants (edited by Kerry S. Walter and Harriet J. Gillett, 1998) the plant scientific community has recently been made aware that some 34,000 species (12.5% of the world's flora) are facing extinction. Because plants are the primary producers in most natural ecosystems, each plant species has dependent upon it approximately 30 other species of organism. It follows that for every plant species that becomes extinct, 30 other species go with it - many of these will be plant pathogens. But this is only part of the problem. With the continuing rapid loss of habitats and ecosystems world-wide, the increased use of fungicides, pesticides and herbicides in agriculture, and the release of genetically modified organisms (GMOs), the threats to pathogen diversity in the wild are immense.

A second, equally important threat concerns the pathogens of cultivated plants, especially those of major crop species. Such pathogens, which are usually held ex situ either in official culture and DNA collections or, very frequently, in personal collections have a central role in revealing genetic diversity in potential breeding material and provide vital screens for the development of new culivars. They are, in addition, the raw material for much of the basic scientific research on life cycles and genetics that generate an understanding of pathogen variation, evolution (in the short term on crops and in the long term in natural plant populations) and population dynamics. Finally, they constitute a potentially significant biotechnological resource of particular importance to the genetic engineer.

This diversity is also under threat. National and international collections are placed at risk by short term funding by governments and agencies and reliance on commercial sources of income. A steady decline in the numbers of pathogen systematists, brought about by ignorance of the importance of systematics and changes in scientific fashion, will undermine the curation of those collections that survive. And finally, a lack of awareness on the part of funders and institution managers of the importance of unique collections built up over a long career by individual plant pathologists and breeders, will lead to significant losses of these irreplaceable resources, especially at a time when institutions must work to short planning horizons, or have limited life.

It is my view that there is an urgent need for plant pathologists to address the following issues.

1. Do we know enough about the diversity and significance of plant pathogen populations in natural ecosystems?

I suggest that we do not. The decline of the "naturalist tradition" in Europe, the increasing concern of governments to fund research that has economic significance rather than being curiosity led and a preoccupation with cells and molecules rather than whole organisms and populations has resulted in a decline rather than an increase in our knowledge of plant diseases among wild populations of plants. In the tropics and subtropics efforts have largely focused on studies of the diversity and ecology of higher plants and animals, with scant attention being paid to pathogens except where they pose a threat to adjacent crop plants. We remain woefully ignorant of the huge diversity of pathogens that affect the algae, the wild plants of the oceans and lakes, despite the fact that c. 50% of all photosynthetic productivity on earth takes place in water.

It is high time that a significant international effort was made to:

• Catalogue the diversity of plant pathogens in natural ecosystems, with particular emphasis being placed upon species-rich ecosystems such as rainforests, grasslands and the oceans. Why is there no "Red Data Book" for pathogens? Do we have enough pathogen systematists?

• Build on the already excellent work on the population genetics of key pathogens in natural ecosystems, including the oceans and lakes, to greatly extend our knowledge in this sphere. Intensify research on the ecology and physiology of the interaction between pathogens and their hosts in wild ecosystems, focusing especially on reproduction and population dynamics.

• Initiate studies on the effects, real or potential, of the release of fungicides, pesticides and GMOs into the environment.

• Consider how studies of pathogens in natural ecosystems may contribute to a better understanding of how plant disease may be controlled in sustainable agricultural systems or may be used in the development of entirely new control strategies for diseases, pests and weeds.

• Consider whether pathogens of wild species should be conserved in situ or ex situ in collections.

2. Are adequate systems in place to ensure the survival, growth and adequate curation of ex situ collections of crop pathogens or their DNA? And is sufficient research effort being directed towards crop pathogen systematics, evolution, genetics and biology?

I suggest that the answers to both questions is "no". The economic, social and political climate in which most of us operate is such that short-termism, cost-cutting and scientific fashion all militate against a "yes" answer to either question.

It is time for a concerted effort to: Assess the true "value", not "cost" of collections of pathogens of crops. Assess the threats to the survival of collections, large and small and work for their preservation, curation and development . Identify the lacunae in our knowledge of crop pathogen biology and genetics, particularly details of life cycles, and give appropriate acknowledgement and funding to research that addresses such issues. Recognise the importance of fungal and microbial systematics and seek funds to support this aspect of research and the training of new systematists (see also 1 above).

3. Is there a need for a policy on the conservation of plant pathogens?

I suggest that among the issues that require discussion are the following: If a conservation policy is developed, how could it operate and what should its limits be? What can be learned from the conservation policies of other societies, such as the British Mycological Society? Are ex situ collections enough, or should the policy embrace in situ conservation?  Would pathogens conserved in natural ecosystems be seen as a threat to crop production? . In the conservation of natural ecosystems, should efforts be focused on those in which important crop relatives continue to co-evolve with important pathogens? Or should a wider view of conservation be taken? What might be the costs and the benefits of national and international conservation policies for plant pathogens? How many pathogen species and how much biodiversity is it necessary to conserve? And what do we mean by "biodiversity" of pathogens?

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