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Symptom  [ Phytopathology ]

Dictionary of botanic terminology - index of names

  A symptom is a plantís visible reaction to the presence of a biotic or abiotic causal agent or disease.  
The fact that diseased plants are in some way different from healthy  plants indicates that there are ways of recognizing plant diseases and the terminology used for description of plant symptoms is really quite simple, not at all like that of, say, human medicine. Plant diseases are frequently given their common names based on the plant part affected, by the way the plant is affected, or by the cause of the disease.
Symptoms of plant diseases include some general types:
1) Hypertrophy (Overdevelopment) of tissue
2) Hypotrophy and/or atrophy (Underdevelopment) of tissue.
3) Death of tissue.
  • Spots: A "spot" is a relatively small, distinct lesion, with definite borders. Most times, we indicate the plant organ affected when describing a plant disease symptom. For example, if the spot is on leaves, it is called a "leaf spot". If the spots are on fruit, it is naturally a "fruit spot".
  • Blights: As spots grow and coalesce, the symptoms may well be described as a "blight". There are gradations from spots to blights and the better term to use may not always be clear.
  • Cankers: again, found mostly on stems and branches, are sunken lesion.
  • Rots: Rots occur when tissue breaks down. Rots lead to a slimy, wet "mush". However, dry rots can occur.
4) Problems with water uptake
  • Wilts: Wilts occur when plants droop.
A good home gardener recognizes symptoms of plant diseases quickly and takes steps to prevent or control them. Hoverer the extremely large number of plant diseases (over 50,000) makes it impossible for any one person to be familiar with all of them but, there are certain facts that help in the identification of plant diseases. The most important is to know the name of the plant that is affected. One can then check known plant diseases to see if a similar condition has ever been reported on that plant.

Useful tip to identify plant disease:
  • Foliage symptoms: Foliage on plants infected with a bacterium or fungus will normally develop first on the older leaves. Virus symptoms develop on the younger leaves. If it occurred in a very short time (overnight), it is probably not a parasitic disease, but is more likely due to some unfavourable environmental condition or chemical.
  • Parasitic diseases:  Symptoms due to a parasitic attack usually do not affect a large percentage of the plants in the early stages, but start in one area and gradually spread to the other plants. And, parasitic diseases usually do not affect several different kinds of plants in one area at one time, even though some disease organisms can attack many different plants.

There is often a tendency for gardeners to immediately suspect a disease when a leaf turns yellow or brown. But, it may just be a normal response. Even evergreens lose their leaves eventually.








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