Diseases in plants can be caused by a number of pathogens and almost all plant species. Therefore, it is difficult to classify plant disease based on one factor only. So plant diseases can be classified in many ways based on the factors involved in the disease inciting (viz., susceptible host, parasite and environment). Plant diseases can be classified as;
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| Leaf yellowing of Malvastrum sp. (viral disease) |
i) On the basis of Causal Organisms
For example,
Diseases caused by bacteria,
Diseases caused by viruses,
Diseases caused by mollicutes,
ii) On the basis of the Type of Plants
For example;
Cereal crop diseases,
Diseases of fruit crops,
Diseases of vegetable crops,
Diseases of ornamental plants
iii) On the basis of their Symptoms
For example;
- Rusts,
- Smuts,
- Powdery Mildews,
- Downy Mildews,
- Leaf blights,
- Vascular wilts,
- Damping off,
- Leaf blights
iv) On the basis of their Occurrence
a) Endemic Diseases
The disease which is present in more or less constantly from year to year in the same area or crop field. In this case the pathogen is well established in the soil or other medium and survives there from season to season.
b) Epiphytotic Diseases ( or Epidemic Diseases)
The diseases which show widespread occurrence in an area but occur periodically. These diseases depends largely on the environmental conditions. In case of epiphytotic diseases, favourable environmental conditions may occur largely but the pathogen may be present irregularly. For example, the incidence of Late blight of potato (Phytophthora infestans).
c) Sporadic Disease
In cases, when epiphytotic diseases occur at very irregular intervals and locations and in relatively few intervals, these are termed as Sporadic diseases.
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