Some host genotypes possess the ability to prevent a pathogen strain from producing disease. Such host lines are called resistant, and this ability is called resistance or disease resistance. The term strain has a similar meaning for the pathogen as line has for the host.
Those lines of a host that are not resistant to the pathogen are called as susceptible.
A successful breeding for disease resistance depends mainly on the following two factors: (i) a good source of resistance, and (ii) a dependable disease test.
Sources of resistance genes may be cultivated varieties, germplasm collections of the crop or wild relatives of the crop.