Phenotypic and Genotypic Characterization of Race TKTTF of Puccinia graminis f. sp. tritici that Caused a Wheat Stem Rust Epidemic in Southern Ethiopia in 2013–14

Abstract

A severe stem rust epidemic occurred in southern Ethiopia during November 2013 to January 2014, with yield losses close to 100% on the most widely grown wheat cultivar, 'Digalu'. Sixty-four stem rust samples collected from the regions were analyzed. A meteorological model for airborne spore dispersal was used to identify which regions were most likely to have been infected from postulated sites of initial infection. Based on the analyses of 106 single-pustule isolates derived from these samples, four races of Puccinia graminis f. sp. tritici were identified: TKTTF, TTKSK, RRTTF, and JRCQC. Race TKTTF was found to be the primary cause of the epidemic in the southeastern zones of Bale and Arsi. Isolates of race TKTTF were first identified in samples collected in early October 2013 from West Arsi. It was the sole or predominant race in 31 samples collected from Bale and Arsi zones after the stem rust epidemic was established. Race TTKSK was recovered from 15 samples from Bale and Arsi zones at low frequencies. Genotyping indicated that isolates of race TKTTF belongs to a genetic lineage that is different from the Ug99 race group and is composed of two distinct genetic types. Results from evaluation of selected germplasm indicated that some cultivars and breeding lines resistant to the Ug99 race group are susceptible to race TKTTF. Appearance of race TKTTF and the ensuing epidemic underlines the continuing threats and challenges posed by stem rust not only in East Africa but also to wider-scale wheat production.

Disease Impact on Wheat Yield Potential and Prospects of Genetic Control

“…The Ug99 race group is not the only cause of the current stem rust problem in East Africa. In Ethiopia, another SrTmp virulent non-Ug99 race TKTTF was detected at trace levels in 2012 on the popular cultivar Digalu and has caused continuing epidemics since 2013 (74). The rapid spread of race TKTTF in Ethiopia and SrTmp variants of Ug99 in neighboring countries has increased rust populations in East Africa, with serious consequences for farmers in the region and enhanced vulnerability globally.…”

“…The SrTmp virulent race TKTTF, within a matter of weeks from detection in 2013, caused severe epidemics on an estimated 20,000-40,000 ha, and yields were reduced to 0.3 t/ha in the worst affected areas, representing >90% losses. Average yield losses on Digalu in three districts at the core of the 2013/14 epidemic were estimated at 51% (74). Continued extensive cultivation of Digalu in 2014/15 due to the lack of seeds of replacement varieties, ineffective fungicide use, and/or the lack of fungicide availability resulted in repeat epidemics on 30,000-50,000 ha, with near complete losses on individual farms and devastating impacts on households.…”

Discovery and characterization of two new stem rust resistance genes in Aegilops sharonensis

“…Recently, a severe, localized stem rust epidemic developed on the variety Digalu in southern Ethiopia during November–December 2013. Digalu carries SrTmp and is resistant to race TTKSK; however, the epidemic was caused by race TKTTF, which is not part of the Ug99 race group (Olivera et al 2015). Deployment of single Sr genes in wheat often leads to the rapid appearance of resistance-breaking strains of Pgt .…”

Wheat in Kenya: Past and Twenty-First Century Breeding

“…f. sp. tritici Eriks) [12] and other related races [13] have reduced Kenya and regional countries to perennial net wheat grain importers. This is in the backdrop of increased consumption needs, estimated at more than 150% of local production [14].…”