Question

Classify of plant diseases on the basis of occurrence

Answer 1

Study of plant dis­eases in relation to their occurrence (interaction of populations of plants, pathogens and environment) is known as epidemiology. There may be infectious disease and contagious disease. A disease which spreads slowly and is incited by a transmissible pathogen is referred as infectious disease, and that which spreads rapidly is a contagious disease.

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Considering from the point of view of occurrence the diseases are often classified as:

Endemic, epidemic or epiphytotic, and sporadic.

A disease which constantly occurs from year to year in moderate to severe form is an endemic disease. Greeneria fruit rot of grape (Vitis vinifera) is an endemic disease in India caused by Greeneria uvicola. But an epidemic disease or epiphytotic disease is the one whose incidence is periodical in wide areas spreading very fast. The term epi­phytotic is rather used in case of plant disease.

The epiphytotic disease is usually very responsive to variations of environmental conditions which actually control its incidence. Like endemic disease, the pathogen may be more or less constantly present but to ensure disease development environmental conditions must be favourable.

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The Epiphytotic Disease incidence is controlled by:

(a) Availability of susceptible host,

(b) Virulence of pathogen,

(c) Rapidity of dissemination of inoculum and host infection,

(d) Rate of production of inoculum; and

(e) Micro- and macro-climatic conditions.

According to their occurrence in crops, the epiphytotic diseases may be of two kinds; the diseases ordinarily endemic but assume epidemic proportions from time to time, and those completely newly introduced in the locality—the exotic diseases.

Wart disease of potato caused by Synchytrium endobioticum is an exotic dis­ease in India. In the former kind, the disease incidence depends mainly on the varia­tions of the climatic conditions. Whereas, the latter is resulted either from a new parasite having been introduced from another country, or from the passage of a para­site of some pre-existing plant of a place to a newly introduced host.

Answer 2

Dear Students,

● Classification of plant diseases on the basis of their occurrence -

Endemic

Epidemic

Pandemic

Sporadic

(1) Endemic diseases -

An endemic disease is a disease that is always present as some form in a certain region.

(2) Epidemic diseases -

An epidemic disease is that disease which occurs periodically in severe form.

(3) Sporadic disease -

Sporadic disease occurs occasionally, singly, or in scattered instances without any known cause.

(4) Pandemic diseases -

Pandemic is the epidemic of disease that has spread across a large region usually multiple continents or even worldwide.

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Answer 3

Dear Students,

● Classification of plant diseases on the basis of their occurrence -

1. Endemic
2. Epidemic
3. Pandemic
4. Sporadic

(1) Endemic diseases -

• An endemic disease is a disease that is always present as some form in a certain region.

(2) Epidemic diseases -

• An epidemic disease is that disease which occurs periodically in severe form.

(3) Sporadic disease -

• Sporadic disease occurs occasionally, singly, or in scattered instances without any known cause.

(4) Pandemic diseases -

• Pandemic is the epidemic of disease that has spread across a large region usually multiple continents or even worldwide.

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