Review of Concepts and Methods of Genetic Characterization and Breeding Wheat for Resistance to Rusts

Abstract

Rust diseases are economically the most important constraints to global wheat production. Breeding for resistance to diseases involves the understanding of genetic systems of both the host and pathogen simultaneously. Knowledge of host-pathogen interaction is essential for breeding disease resistant crops, because both host and pathogen populations are genetically diverse. Resistance to rust diseases can be classified into two broad categories; seedling/ all stage resistance (ASR) and adult plant resistance (APR). All stage resistance genes confer resistance at all growth stages against avirulent pathogen isolates. However, ASR genes often succumb to evolution in pathogen populations, whereas APR genes are expressed at later growth stages of the plant, show uniform response to all races of the pathogen and do not encourage pathotypic evolution and the nature of resistance they offer is usually durable. Characterization of resistance to rusts involves gene postulation (multi-pathotype test), genetic analyses and identifying the number and location of the gene(s) conferring resistance. Chromosomal location and mapping genes have been done using cytogenetic analysis; however, since 1990s the advancement of molecular genetics and biotechnology enabled to replace the tedious, time, labor and resource consuming cytogenetic analyses method of locating genes using molecular mapping techniques.