Marker-Assisted Breeding for Resistance Against Wheat Rusts

Leaf, stem and stripe rust diseases seriously threaten wheat production worldwide. The obligate biotrophic rust pathogens are highly capable of producing new virulent races that can overcome resistance. To defy the emerging threat of rusts in wheat, attempts are going on at global level for identification of pathotypes, new sources of resistance and deployment of resistant varieties for management of these rusts. Several rust resistance genes (>200) and their associated molecular markers are available to breeders for their use in rust resistance breeding programme. Molecular markers have been extensively used in wheat breeding programmes for various reasons, of which linkage and QTL map being on the top list. Linkage maps depict the presence of major genes and QTLs on chromosomal regions. Molecular markers associated with many effective resistance genes are now increasingly available and have been successfully utilized in many wheat breeding programmes. Marker systems like SSR, STS, SCAR, DArT and SNPs are now popularly being used because of their robustness. MAS and more traditional screening methods like seedling resistance test (SRT) against the rust pathotypes are often complementary, and both are utilized depending on the generation. MAS has important application when two or more resistance genes against particular rust need to be pyramided in a single wheat genotype. In such cases where screening with the pathotypes is not able to confirm the presence of two or more resistance genes conferring resistance against all the pathotypes of the disease, MAS helps in the selection. The various approaches presently being used for MAS has been discussed in this chapter along with the successful examples of mapping various rust resistance genes and their introgression into elite wheat cultivars using various marker-assisted breeding strategies.