Tens of thousands of diseases affect cultivated and wild plants.
On average, each kind of crop plant can be affected by a hundred or more plant
diseases. Some pathogens affect only one variety of a plant. Other pathogens
affect several dozen or even hundreds of species of plants. Plant diseases are
sometimes grouped according to the symptoms they cause (root rots, wilts, leaf
spots, blights, rusts, smuts), to the plant organ they affect (root diseases,
stem diseases, foliage diseases), or to the types of plants affected (field
crop diseases, vegetable diseases, turf diseases, etc.).
One useful criterion for
grouping diseases is the type of pathogen that causes the disease. The
advantage of such a grouping is that it indicates the cause of the disease,
which immediately suggests the probable development and spread of the disease
and also possible control measures. On this basis, plant diseases are
classified as follows:
I. Infectious, or biotic, plant diseases
1. Diseases caused by fungi.
2. Diseases caused by prokaryotes (bacteria and mollicutes).
3. Diseases caused by parasitic higher plants and green algae
4. Diseases caused by viruses and viroids.
5. Diseases caused by nematodes.
6. Diseases caused by protozoa.
II. Noninfectious, or abiotic, plant diseases.
1. Diseases caused by too low or too high a temperature
2. Diseases caused by lack or excess of soil moisture
3. Diseases caused by lack or excess of light
4. Diseases caused by lack of oxygen
5. Diseases caused by air pollution
6. Diseases caused by nutrient deficiencies
7. Diseases caused by mineral toxicities
8. Diseases caused by soil acidity or alkalinity(pH)
9. Diseases caused by toxicity of pesticides
10. Diseases caused by improper cultural practices
