Explain methods of breeding for disease resistance.

Breeding is carried out by the conventional breeding techniques or by mutation breeding.
The conventional method of breeding for disease resistance is that of hybridisation and selection. It.s steps are essentially identical to those for breeding for any other agronomic characters such as high yield.
The various sequential steps are screening germplasm for resistance sources, hybridisation of selected parents, selection and evaluation of the hybrids and testing and release of new varieties. Some crop varieties bred by hybridisation and selection for disease resistance to fungi, bacteria and viral diseases are released. Some of them are shown below.

Conventional breeding is often constrained by the availability of limited number of disease resistance genes that are present and identified in various crop varieties or wild relatives.
Inducing mutations in plants through diverse means and then screening the plant materials for resistance sometimes leads to desirable genes being identified.
Plants having these desirable characters can then be either multiplied directly or can be used in breeding.
Many other breeding methods that are used are selection amongst somaclonal variants and genetic engineering.