Classification of plant diseases

Plant diseases are variously grouped according to the host plant, their part affected, nature of occurrence, causal agent, on the basis of symptoms, etc. Classification of plant disease based on the causal agent is, however, most extensive and suitable.




Classification of plant diseases
Plant diseases

Classification of plant diseases according to the causal agents

  • Nonparasitic (Environmental factors)
      Diseases incited by:
    1. Low temperature
    2. High temperature
    3. Deficient oxygen
    4. Mineral deficiency | Potassium | Boron | Nitrogen | Calcium
    5. Mineral excess
    6. Unfavorable soil moisture content
    7. Exposure of toxic materials
    8. Injurious atmospheric gases
    9. Lightning injury
  • Parasitic (Biological)
    • Diseases incited by animals:
      1. Nematodes
      2. Insects
      3. Protozoa
      4. Birds
      5. Rodents and other animals
    • Diseases incited by plants:
      1. Fungi
      2. Mycoplasmas
      3. Bacteria
      4. Algae
      5. Angiosperms
    • Diseases incited by virus:
      1. RNA viruses
      2. DNA viruses


Classification of plant diseases according to their severity and occurrence

Endemic diseases

Endemic disease is more or less constantly present in a confined geographical area or region in a moderate or severe form. Local environmental conditions of the area are favorable for the survival of inoculums.
Example:
  • Wart disease of potato caused by Synchytrium endobioticum is endemic in Darjeeling of West Bengal, India.

Epidemic or epiphytotic diseases

The term 'epidemic' is used for the diseases of humans, while 'epiphytotic' is used for plant diseases. Epidemic or epiphytotic diseases are prevalent in a wider area but become destructive periodically. These diseases are very much responsive to environmental conditions.
Example:
  • Inoculums of late blight of potato caused by Phytophthora infestans is present in an area, but disease becomes destructive, only when temperature and humidity become favorable.


Sporadic diseases

Sporadic diseases occur at very irregular intervals and locations. In real sense, this belongs to epiphytotic disease, but has fewer instances and is comparatively less destructive.
Example:
  • Angular leaf spot of cucumber.

Pandemic diseases

Pandemic diseases occur over large geographical areas including different continents and cause heavy economic loss.
Example:


Classification of plant diseases according to cycle of reccurance

On the basis of number of cycles a disease can repeat in the same season, disease can be of following types:

Monocyclic diseases

  • Pathogen infects only once in a growing season of host.
  • There is no secondary inoculum. Disease is caused only by primary inoculum.
  • The severity of disease is increased year by year.
  • Soil-borne diseases are mostly monocyclic.
  • Also known as simple interest disease.
  • Example: Wilt of arhar caused by Fusarium oxysporum f. udum Butler

Polycyclic diseases

  • Pathogen infects several times per growing season.
  • Pathogenesis is caused by both primary and secondary inoculums.
  • Primary inoculum consists of sexual dormant structures or sclerotia.
  • Airborne diseases are mostly Polycyclic.
  • Also known as compound interest disease.
  • Example: Stem rust of wheat caused by Puccinia graminis f. sp.tritici.

Polyetic diseases

  • Pathogen does not infect every year.
  • Pathogen takes several years to produce inoculum.
  • The amount of inoculum is increased over several years rather than within a year.
  • Also known as a multiyear disease.Pathogen survives on perennial hosts.
  • Example: Powdery mildew of apple Podosphaera leucotricha.

Content first created on 06-05-2021
last updated on 02-12-2024