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Return to
Lead Story

Biodiversity and
Plant Pathogens
and Conservation

by Dr. David Ingram

Participate in an
Discussion on
Plant Pathogen Conservation

British Mycological
Society Draft Policy
On Conservation
of Fungi

Six Reasons to
Value the Biodiversity
of the Earth

Vole Power:
Herbivores Prefer
Diseased Plants

A Study of Two
Oak Species and
Powdery Mildew

What is
Plant Pathology?

   Related Reading:
Potato Late Blight and
   the Irish Potato Famine
   Why Europeans
   Drink Tea

   Meltdown for

Link to the site of the
7th International
Congress of Plant

The American
Phytopathological Society
3340 Pilot Knob Road
St. Paul, MN
55121-2097 USA
e-mail: aps@scisoc.org

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Case Study of a Plant Disease
in a Natural Setting

by Avice Hall, University of Hertfordshire, UK

In the UK there are two species of deciduous oak, Quercus robur and Quercus petraea. The two species have a slightly different but overlapping
bareoak.JPG (37861 bytes) distribution. Both are wind pollinated trees and there is great potential for the production of fertile hybrids. Oaks are said to have more species of plant, animals and microorganisms associated with them than any other species in Britain, thus they almost form an ecosytem in
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P. Beales 1997
their own right. From June each year, there is infection of young leaves by oak powdery mildew, Microspheara alphitoides. However, Q. robur is more susceptible than Q. petraea and hybrids show intermediate susceptibility.

This disease illustrates well some of the characteristics of plant diseases in natural communities where man has little influence. It gives a hint of the roles that plant pathogens play in ecosystems, and why there needs to be a Biodiversity Action Plan to conserve even these disease causing organisms.

1) One species is more susceptible than the other.

2) Whilst many individual leaves on a tree may be infected and die, M. alphitoides alone is rarely a cause of tree death.

3) The hybrids show a complete range of susceptibility.

4) When hybrid acorns germinate they often form a monoculture of seedling oaks near the parent tree. Some become heavily diseased  and mildewontwig.JPG (30449 bytes)die, whilst others (presumably with more resistance characteristics) live and grow to maturity.

5) Oak powdery mildew and its hosts are a good example of how hosts and pathogens can co-evolve over many millenia and remain in balance provided that there is an absence of interference from man.

Conservation of host and pathogen are necessary to preserve the total ecosystem. To eradicate the pathogen would lead to a series of unpredictable changes in the evolution of oaks and their ecosystem. 

Copyright 1998 by The American Phytopathological Society
Copyright 1998 by The British Society for Plant Pathology