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 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. A susceptible variety may be able to escape the attack of a pathogen due to either the absence of the pathogen or the lack of environmental conditions necessary for a disease to occur. It is important for growers to understand their particular needs before choosing a variety.