The ability of plants to suppress or retard the activities of a specified pest or pathogen. Also, the ability of plants to withstand a specific environmental or chemical stress.

Tolerance:

The ability of plants to endure a specified pest, pathogen, environmental pressure or chemical stress. A tolerant variety will sustain less damage than a susceptible variety when grown under the same conditions.

Susceptibility:

The inability of plants to restrict the activities of a specified pest or pathogen. Also, the inability to withstand a specific environmental or chemical stress.

A word of caution should be noted concerning disease resistance, tolerance and susceptibility.

It should be recognized that the degree of resistance or tolerance of a variety to a disease in influenced by many factors. The aggressiveness of strains of the pathogen (disease causing organism) to which the plant is subject will influence the disease reaction. The amount of the pathogen present can also influence the resistance or tolerance of a variety. Environmental conditions are extremely important in disease development. Adverse environmental conditions may allow the pathogen to overcome the resistance or tolerance which is bred into a variety. Finally, new races or strains of the pathogen may occur which allow it to attack the plant.