Throughout the history, stem rust has been considered a major threat to the wheat production. The spread of stem rust race Ug99 and variants are threat to worldwide wheat production and efforts are being made to identify and incorporate resistance. A primary source of concern at present is that Ug99 (TTKSK and its variants TTKST and TTTSK) has overcome major sources of stem rust resistance genes eg Sr31, Sr38 and other important gene complexes which confer resistance to stem rust. Deployment of cultivars with broad spectrum rust resistance is the only environmentally viable option to combat these diseases. Therefore, identification, mapping and deployment of effective resistance genes are critical components of global efforts to mitigate this threat. Identification and introgression of novel sources of resistance is a continuous process to combat the ever evolving pathogens. Few stem rust resistance (Sr) genes derived from the primary and secondary gene pool of wheat confer resistance to TTKSK and its variants. Inheritance of stem rust resistance in wheat can be either qualitative or quantitative. While quantitative disease resistance is believed to be more durable, it is more difficult to evaluate as it is expressed in mature plants, i.e. adult plant resistance (APR). Breeding resistant cultivars is the most realistic approach to protect wheat from stem rust. Deployment of combinations of effective genes â€œstackedâ€ or â€œpyramidedâ€ in combination with APR genes should improve the durability of resistance in commercial cultivars by reducing the probability of corresponding simultaneous mutation events in the pathogen. Gene pyramiding is facilitated by the ability to use molecular markers closely or completely linked to resistance genes.Though Ug99 type of races have posed a threat to the wheat cultivation worldwide, several developing countries of South and West Asia have taken proactive steps to meet this challenge.
Keywords: stem rust, UG-99, Sr-24, QTL mapping, Durable resistance, Shuttle Breeding, BGRI, MAS, MAB, MABC