Current status, likely migration and strategies to mitigate the threat to wheat production from rzace Ug99 (TTKS) of stem rust pathogen.

Abstract

Stem or black rust, caused by Puccinia graminis tritici, has historically caused severe losses to wheat (Triticum aestivum) production worldwide. Successful control of the disease for over three decades through the use of genetic resistance has resulted in a sharp decline in research activity in recent years. Detection and spread in East Africa of race TTKS, commonly known as Ug99, is of high significance as most wheat cultivars currently grown in its likely migration path, i.e. to North Africa through Arabian Peninsula and then to Middle East and Asia, are highly susceptible to this race and the environment is conducive to disease epidemics. Identifying/developing adapted resistant cultivars in a relatively short time and replacing the susceptible cultivars before rust migrates out of East Africa is the strategy to mitigate potential losses. Although several alien genes will provide resistance to this race, the long-term strategy should focus on rebuilding the 'Sr2-complex' (combination of slow rusting gene Sr2 with other unknown additive genes of similar nature) to achieve long-term durability. A Global Rust Initiative has been launched to monitor the further migration of this race, facilitate field testing in Kenya or Ethiopia of wheat cultivars and germplasm developed by wheat breeding programmes worldwide, understand the genetic basis of resistanceespecially the durable type, carry out targeted breeding to incorporate diverse resistance genes into key cultivars and germplasm, and enhance the capacity of national programmes. A few wheat genotypes that combine stem rust resistance with high yield potential and other necessary traits have been identified but need rigorous field testing to determine their adaptation in target areas.

The coffee rust crises in Colombia and Central America (2008–2013): impacts, plausible causes and proposed solutions

“…In all cases, breeders have to consider the possible emergence of new coffee rust races, as shown by the appearance of the Ug99 strain of stem rust that can attack all cultivars of wheat grown in the world (Singh et al 2006). The wheat stem rust (Puccinia graminis f. sp.…”

Genetic analysis of rust resistance genes in global wheat cultivars: an overview

“…tritici (Pgt) is a major biotic constraint in most of the wheat-growing areas in the world and causes yield losses of up to 100% during epidemic outbreaks [85]. Ug99, a new virulent stem rust race, was first identified in Uganda in 1999 [86] and then spread to Kenya in 2001 and to Ethiopia in 2003, following the migration path suggested by Singh et al [87]. Currently, it is a major threat to global wheat cultivation.…”

“…Among these genes, at least 27 genes, including Sr2 (Yr30), Sr13, Sr21, Sr22, Sr24, Sr25, Sr26, Sr27, Sr28, Sr32, Sr33, Sr35, Sr36, Sr37, Sr39, Sr40, Sr42, Sr44, Sr45, Sr46, Sr47, Sr51, Sr52, Sr53, Sr55 (Lr67/Yr46/ Pm46), Sr57 (Lr34/Yr18/Pm38), and Sr58 (Lr46/Yr29/Pm39), are effective or partially effective against the Ug99 race group [91][92][93][94][95][96][97][98][99][100]. Among these 27 genes, Sr2, Sr13, Sr22, Sr25, Sr26, Sr35, Sr39 and Sr40 were reported to be the most effective against Ug99 [87,[101][102][103]. A brief description of the details of these genes is given in Table 4.…”

“…Detailed genetic characteristics of the above-described stem rust resistance genes are shown in Table 4. One of the more effective stem rust resistance genes Sr2 is a catalogued adult plant stem rust resistance gene in wheat [34] and has been shown using SSR markers to be located in a region on the short arm of chromosome 3B [125] [87,126], Due to its ability to confer durable and broad-spectrum resistance, the Sr2 gene has been used to improve resistance against stem rust diseases in several popular International Maize and Wheat Improvement Centre (CIMMYT) varieties cultivated worldwide [129]. Generally, Sr2 confers moderate levels of resistance against Ug99 (generating an approximate 30% reduction in disease severity); however, strong resistance can be achieved when it is combined with other unknown genes, such as the Yr30, Lr27 and Pbc genes of the Sr2-complex.…”

Fine mapping and characterization of Sr21, a temperature-sensitive diploid wheat resistance gene effective against the Puccinia graminis f. sp. tritici Ug99 race group

“…Unfortunately, an isolate of Pgt was reported in Uganda in 1999 (Ug99) that is virulent to plants carrying the wheat resistance genes currently deployed in most of the large wheat growing regions of the world (Pretorius et al 2000;Singh et al 2006). This isolate was classified as race TTKSK according to the North American system for Pgt race nomenclature (Jin et al 2007;Jin et al 2008).…”