Alternate host

Many pathogens have more than one host. In the absence of one host, the pathogen can survive on another host of related or unrelated plant families. Alternate hosts are the plants belonging to the unrelated family of the primary host.
Alternate host
Croton is an alternate host of Bhindi Yellow Vein Mosaic Virus (BYVMV)

In absence of okra, yellow vein mosaic virus survives in Croton and Ageratum, which are alternate hosts for the virus.


The tendency of an organism (here a biocontrol agent) to object or oppose the activity (growth and development) of another organism (here a pathogen) is called antagonism. In ecological sense, antagonism is negative interaction.


Any malfunctioning of host cells and tissues that results from continuous irritation by a pathogenic agent or environmental factor (not by direct physical injury) and leads to the development of symptoms.

Biocontrol agent

Natural enemies of pests are known as biocontrol agents or biological control agents. Biocontrol agents are any organisms, but for man itself. Biocontrol agents inhibit the growth of pests or kill them through action of competition, predation, antagonism, parasitism or hyperparasitism.


Competition is a situation, where two organisms (pests and biocontrol agents) try to get something, which is common for both. A pest and biocontrol agent compete for space and nutrition.

Disease cycle

The chain of events involved in disease development, including the stages of development of the pathogen and the effect of the disease on the host. Disease cycle of a pathogen includes pathogenesis, reproduction, dispersal and dormancy.

Emulsifiable Concentrate (EC)

ECs are transparent oily liquid formulations, in which pesticides or active substances are dissolved in organic solvent, such as toluene, benzene, xylene, etc. Sometimes, this may contain surfactant also. These preparations when diluted in water before application, form oil-in-water emulsion and oil contains the pesticide.
EC are prepared because the acidic salts of pesticides, which are water soluble, may react with metallic ions in the water and form precipitate and clog the spraying instruments.


Study of disease in plant populations. It requires biological, statistical, agronomic and ecological perspectives.


A widespread and destructive outbreak of a disease of plants (= epidemic). It can cause huge losses in yield of crops as well threatening to wipe out an entire species in the area.


The determination and study of the cause of a disease.

Facultative parasite

A saprophyte having the ability to be a parasite.

Facultative saprophyte

A parasite with the ability to be a saprophyte. (= hemibiotrophs)


A compound toxic to fungi.


A compound that prevents fungus growth without killing the fungus.


The pathogen(s) that lands on or is otherwise brought into contact with the plant is called the inoculum. The inoculum is any part of the pathogen that can initiate infection.


Located between the spaces of two or more cells.


Located within a cell.


An organism having capability of parasitizing a fungus. The phenomenon of parasitizing a fungus by other fungus is mycoparasitism. Mycoparasites are utilized as biocontrol agents.

Obligate parasite

A parasite that in nature can grow and multiply only on or in living organisms.

Obligate symbiosis

Obligate symbiosis is when one or both the symbionts can not survive without each other.


An organism living on or in another living organism (host) and obtaining its food from the latter.


An entity that can incite disease.


The process of inciting a disease. Pathogenesis is the stage of disease in which the pathogen is in intimate association with living host tissue.


The capability of a pathogen to cause disease.


It is a kind of harmful biological interaction, whereby an organism (Predator) kills others (Prey).

Primary infection

The first infection of a plant by the overwintering or oversummering pathogen.

Primary inoculum

The overwintering or oversummering pathogen, or its spores that cause primary infection.


Possessing qualities that hinder the development of a given pathogen; infected little or not at all.


Rhizosphere is a narrow zone of soils around the roots, which is directly affected by the activities of roots. It is a highly dynamic region, where microbial populations are under high influence of root secretions.
The term rhizosphere was coined by Hilter in 1904.

Secondary infection

Any infection caused by inoculum produced as a result of a primary or a subsequent infection; an infection caused by secondary inoculum.

Secondary inoculum

Inoculum produced by infections that take place during the same growing season.


Lacking the inherent ability to resist disease or attack by a given pathogen; nonimmune.


The external and internal reactions or alterations of a plant as a result of a disease.

Systemic resistance

Systemic resistance is the ability of resistant plants to de-novo synthesize certain chemicals to defend the un-affected parts of the plant far away from the site of infection.

Content first created on 01-05-2021
last updated on 25-09-2022