by Avice Hall, University of Hertfordshire, UK
Plant Pathology is the study of the diseases and disorders of plants. Disease can be defined as a harmful deviation from normal functioning of the physiological processes caused by an infectious agent. In the case of plant diseases, the causal agent maybe a fungus, virus, bacterium or a parasitic flowering plant. (A 'harmful deviation' caused by a non-infectious agent, for example, herbicide or nutrient deficiency, is a disorder.)
An example of a rust fungus on a bean leaf.
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An example of a parasitic
flowering plant, bloomrape.
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Much of the time plant pathologists study diseases of crop plants. These diseases have had a huge impact on crops and subsequently on human history. One hundred and fifty years ago the potato crops of much of Europe including Ireland were devastated by the potato blight fungus, Phytophthora infestans, an introduced pathogen on a non-native crop. The ravages of this disease lead to 1 million deaths and 1,500,000 emigrations from Ireland alone. One hundred years ago the coffee rust fungus, Hemileia vastatrix, caused such devastation in the coffee plantations of what is now Sri Lanka that all coffee was dug up and replaced with tea. Fifty years ago an epidemic of brown spot on rice, caused by Cochliobolus miyabeanus, in what is now Bangladesh led to many thousands of deaths from starvation. On the 5th of May this year, a headline in the British newspaper proclaimed 'Meltdown for Chocoholics'. Further reading revealed that the culprits for this crisis were two diseases of cocoa, witches broom and black pod.
Most plant pathologist spend their time studying several of the thousands of diseases of crop plants and working to limit the damage caused by these infectious agents. Eradication may be aimed at removing completely the causal agent of a particular disease, or under some circumstances, the eradication program may be aimed at the alternate host of the pathogen (the infectious agent frequently survives the intercrop period on a totally unrelated host, the alternate host). Eradication of this host removes an essential part of the pathogen's lifestyle. Examples of this include the removal of Ribes spp. to control White Pine Blister rust, or barberry to control black stem rust of wheat. Grubbing up a diseased plant and burning it is a very effective control method.
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Puccinia graminis on barberry |
If this is the case do 'Conservation' and 'Biodiversity' have anything to do with Plant Pathology? Or are Plant Pathologists the only professionals on earth paid to eradicate rare and endangered species and not to be involved in conservation or Biodiversity Action? While there are some conservation initiatives for fungi (mainly aimed at macro fungi and not plant pathogens) there is virtually nothing that involves the conservation of fungal plant pathogens, bacteria or viruses. The World Health Organization rejoiced when smallpox was eradicated as a disease, but some samples of the causal agent have been 'conserved' for future reference.
What should the attitude of Plant Pathologists be towards conservation and biodiversity initiatives? Read on and interact with this site.
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