Introduction

• It is the third link in the infection chain after survival and dispersal of inoculum
• Entry and colonization of pathogen in the host tissues is known as establishment and the infective propagules coming in contact with the host are known as inoculum.

Inoculum potential: It is the inoculum needed for successful infection. It is a function of inoculum density and their capacity.

Def:It is defined as the energy of growth of a parasite available for infection of a host at the surface of the host organ to be infected (Garret, 1960).

The success of process of infection depends on:

1. Host factors :

• Susceptibility of host: It is genetically controlled by DNA and it is an inheritable character which is transmitted from parents to off springs.

• Disease proneness of the host: It is decided by the external factors such as host nutrition, i.e., more nitrogen application makes the host more susceptible and more potash application leads to less susceptibility.

2. Pathogen factors :

• Virulence / aggressiveness of the pathogen: It is determined by genetic material which is inheritable.
• High multiplication rate of the pathogen: Chances of infection increases with high rate of multiplication. High birth rate and low death rate is highly essential for successful infection.
• Proper inoculum potential: In case of specialized pathogens very few or even one spore is capable of causing infection successfully, whereas, non-specialized pathogens require high density of inoculum on the surface of susceptible host for successful infection.

3. Environmental factors:

Environmental conditions such as temperature, relative humidity, moisture, etc., are very important for survival, dissemination and infection process