Detection of Variants of Wheat Stem Rust Race Ug99 (Puccinia graminis f. sp. tritici) in Zimbabwe and Mozambique

Abstract

The migration of Ug99 variants of Puccinia graminis f. sp. tritici is of concern to global wheat production (1). Seven races have been characterized in the Ug99 lineage (3), three of which occur in South Africa (4). During surveys of wheat fields for Ug99 in Zimbabwe and Mozambique in August and September 2010, high stem rust severities were found at Chiredzi, Chisumbanje, and Birchenough in Zimbabwe and at Rotanda in Mozambique. Stem rust was widespread in the lowlands (<800 m above sea level) of Zimbabwe and trace amounts were present in the mid-altitude areas. In Mozambique, stem rust was only observed at Rotanda (sample Moz1001). Collections from Chiredzi (samples Zim1004 and Zim1005), Chisumbanje (Zim1006), and Birchenough (Zim1009 and Zim1010) yielded viable urediniospores for infection studies. According to race analysis conducted on seedlings of the North American stem rust differential set (2) in a greenhouse at 18 to 25°C, Zim1005 and Zim1006 were typed as PTKST and Zim1004 and Zim1009 as TTKSF. Both TTKSF and PTKST were detected in the Zim1010 sample. Race analysis experiments were conducted three times. Urediniospores of isolate Moz1001 were not viable in infection studies, but yielded fungal DNA for simple sequence repeat (SSR) analysis. Using eight selected SSR primer combinations (4), all six isolates clustered within the Ug99 lineage. Isolates Zim1005, Zim1006, Zim1009, Zim1010, and Moz1001 and the stem rust control races TTKSF, TTKSK, and PTKST grouped into two main clusters, with Zim1009 and Zim1010 clustering together and sharing 88% similarity with the rest of the isolates. Zim1005 and Zim1006 were identical to TTKSF and TTKSK, respectively. Zim1004 shared 96% genetic similarity with the TTKSP control, with these two sharing 74% genetic similarity with the remaining isolates. The SSR data correlated with the infection data, except for Zim1004, which was typed as TTKSF but clustered close to TTKSP. Wheat cvs. SC Nduna, SC Shine, SC Stallion, SC Smart, Kana, Insiza, and Dande are predominant in Zimbabwe. Cv. SC Stallion and other unidentified cultivars were susceptible to P. graminis f. sp. tritici in the field in Zimbabwe. In Mozambique, the tall, local cv. Sitsonko was susceptible to P. graminis f. sp. tritici but no infections were observed on SC Nduna or SC Shine. The similarity in P. graminis f. sp. tritici races in Zimbabwe, South Africa, and Mozambique suggests that inoculum is exchanged within the region and explains the detection of race PTKST in South Africa in 2009. Trajectory models showed winds originating at Birchenough in October 2009, where stem rust was observed, passing directly over KwaZulu-Natal, South Africa within 48 to 72 h. Race PTKST was confirmed from collections in KwaZulu-Natal in November 2009 (4). The confirmation of Sr31 virulence in race PTKST in Zimbabwe is important because it provides new geographical records for an Ug99-related race and puts Southern African cultivars with 1B.1R resistance at risk. References: (1) D. Hodson. Euphytica 179:93, 2011. (2) Y. Jin et al. Plant Dis. 92:923, 2008. (3) R. F. Park et al. Euphytica 179:109, 2011. (4) B. Visser et al. Euphytica 179:119, 2011.

Breeding Wheat for Rust Resistance: Conventional and Modern Approaches

“…In 2007, incidence of Ug99 was observed in Iran (Nazari et al, 2009). Original strains of Ug-99 appeared that are further contagious to Sr36 (Jin et al, 2009), Sr24 (Mukoyi et al, 2011) and SrTmp (Newcomb et al, 2016) afterward implanting more varieties susceptible. The prevalence and distribution of Sr31-virulence variants in the Ug99 in East Africa and additional virulent variants instigating local eruptions and epidemics in Ethiopia (Olivera et al, 2015), Central Asia (Shamanin et al, 2018) and Europe (Lewis et al, 2018), entitles that the disease is emerging as a threat to wheat cultivation in wheat production zones.…”

Combating Ug99 - Current Scenario

“…Development and proliferation of Ug-99 race group posed hazard to production of wheat seriously worldwide (Singh et al, 2011). Novel variants of Ug-99 emerged that are additional virulent to Sr24 (Mukoyi et al, 2011), Sr36 (Jin et al, 2009), and SrTmp (Newcomb et al, 2016) subsequently inserting more cultivars vulnerable. The incidence and spread of Sr31-virulence strains in the Ug-99 race group in Eastern Africa and other virulent strains causing epidemics and local eruptions in Ethiopia (Olivera et al, 2015), Europe (Lewis et al, 2018) and Central Asia (Shamanin et al, 2018), designates that the disease is developing as a hazard to wheat production in major wheat production regions.…”

“…The Ug-99 race group, was infectious on almost all the wheat varieties cultivated everywhere in the world (Afzal et al, 2015). Variants of Ug-99 have spread all over southern and eastern Africa, Zimbabwe, Tanzania, Iran and in Egypt (Pretorius et al, 2010;Mukoyi et al, 2011;Hale et al, 2013;Nazari et al, 2009;Patpour et al, 2016). The regional epidemic of wheat stem rust in Germany in 2013 (Olivera et al, 2012) was proceeded by a sequence of periodic occurrence in republics incorporating UK, Denmark, and Sweden (Hovmøller et al, 2019).…”

Registration of ‘Runde’ spring bread wheat cultivar

“…In Zimbabwe, leaf rust (caused by Puccinia triticina) is present in all the wheat-growing areas, and stem rust (caused by Puccinia graminis f. tritici) is common in the lowveld region (Mutari et al, 2009(Mutari et al, , 2010(Mutari et al, , 2011(Mutari et al, , 2012. In Zimbabwe, most of the old and current commercial wheat cultivars are now susceptible to the current races of leaf and stem rust, although no severe epidemics have been observed before (Mutari et al, 2009(Mutari et al, , 2010(Mutari et al, , 2011(Mutari et al, , 2012Mukoyi et al, 2011;Pretorius et al, 2015). The reasons for the breakdown of rust resistance in some cultivars grown in Zimbabwe could be attributed to the evolution of new races which overcome genetic resistance.…”