First Report of Ug99 Race TTKTT of Wheat Stem Rust (Puccinia graminis f. sp. tritici) in Iraq

Abstract

A wheat rust survey was conducted in Iraq in 2019 and collected 27 stem rust (caused by Puccinia graminis Pers.:Pers. f. sp. tritici Erikks. & E. Henn.) samples. Seven samples were viable, and they were tested for races of P. graminis f. sp. tritici at the Regional Cereal Rust Research Center (RCRRC) in Izmir, Turkey under strict quarantine procedures. Two 0.5 cm segments of each infected stem sheath were incubated in a petri dish at 20°C for three hours for re-hydration of urediniospores, which were multiplied on 10-day old seedlings of susceptible cultivar Morocco grown in a spore free growth chamber at 18°C and 16 hours light. Inoculated seedlings underwent a dew period at 18°C for 16 hours dark and 8 hours fluorescent light and 95% relative humidity. Three days after moving the pots to a growth chamber with eight hours dark at 18°C and 16 hours light (300 µmol m-2s-1), each pot was covered using a cellophane bag. Bulk urediniospores of each collection were collected 14 days post-inoculation from a cellophane bag using a mini cyclone spore collector connected to a gelatin capsule. One ml of 3M Novec™ oil was added to each capsule, and spores were inoculated onto 20 North American stem rust differential lines using the standard procedures (Jin et al. 2008). Pre-inoculation, inoculation, incubation, and post-inoculation conditions were the same as above. Seedling infection types (ITs) were recorded 14 days post-inoculation using 0 to 4 scale (Stakman et al. 1962). Race designation followed the five- letter code nomenclature described by Jin et al. (2008). Out of the seven samples, four were typed as TKKTF, two as TKTTF, and one collected from an advanced breeding bread wheat line “Shahoo 2” (Inqalab 91*2/Tukuru) in a trial site at Halabja governorate showed mixed ITs of 11+ and 3+ for lines carrying Sr11, Sr24, Sr36, and Sr31. Three single pustule (SP) isolates were developed from the IT of 3+ pustules collected from the Sr31 tester line, and one SP isolate was developed from the IT 11+ pustule collected from the Sr11 source. After spore multiplication, the SP-derived isolates were inoculated on the 20 North American differential lines. To confirm virulence/avirulence on Sr24, Sr31, and Sr36, cultivars Siouxland (PI 483469, Sr24+Sr31) and Sisson (PI 617053, Sr36+Sr31) were also inoculated. All seedling assays were repeated three times. The three SP isolates virulent on Sr31 were designated as race TTKTT, and the SP isolate virulent on Sr11 was designated as TKTTF. Seedling ITs of 3+ and 0; were recorded for Siouxland and Sisson against TTKTT, respectively, and both cultivars showed IT of 1+ against TKTTF. Race TKTTF was similar to TKKTF except for additional virulence on Sr36, and TTKTT differed from the other two races being virulent on Sr24 and Sr31. DNA analysis of three TTKTT isolates from Kenya and the TTKTT isolate from Iraq using a diagnostic qPCR assay developed by the USDA-ARS Cereals Disease Laboratory (Ug99 RG stage 1, Szabo unpublished) confirmed that all tested isolates belonged to the Ug99 lineage. Race TTKTT was first reported from Kenya in 2014 (Patpour et al. 2016), and in 2018 from Ethiopia (Hei et al. 2020). We report the first detection of TTKTT in Iraq and the Middle East region. This represents only the third instance of a member of the Ug99 race group outside of Africa since first detection of race TTKSK in Yemen in 2006, and Iran in 2007 (Nazari et al. 2009). The continued spread of stem rust races with complex virulence and the increasing frequency and early onset of stem rust infections in the Middle East is a cause for concern. Continuous support for rust surveillance and race typing in this region remains crucial. References: Hei, N. B., et al. 2020. Plant Dis. 104:982. Jin, Y., et al. 2008. Plant Dis. 92:923-926. Nazari, K., et al. 2009. Plant Dis. 93:317. Patpour, M., et al. 2016. Plant Dis. 100:522. Stakman, E. C., et al. 1962. Identification of physiological races of Puccinia graminis var. tritici. U. S. Dep. Agric. ARS E-617.

Geographical Correlation and Genetic Diversity of Newly Emerged Races within the Ug99 Lineage of Stem Rust Pathogen, Puccinia graminis f. sp. tritici, in Different Wheat-Producing Areas

“…Previously, Hasan and Abou-Zeid [ 25 ] reported that lines Sr31, Sr24, Sr38, and Sr36 were the most resistant genes, and Abebe et al [ 26 ] reported that lines Sr24 and SrTmp were effective for all tested isolates; however, our findings do not support this point of view. Taken together, we suggest that changes in the behavior of some lines, i.e., Sr24 , Sr31, Sr36, and Sr38 , are responsible for resistance and had to be interpreted, especially with the first identification of the Ug99 [ 15 ].…”

“…Moreover, Ug99 (TTKSK) of wheat stem rust fungus was reported in Egypt in 2020 [ 14 ]. Additionally, the Ug99 race TTKTT of wheat stem rust was recently reported in Iraq [ 15 ].…”

Irrigation can create new green bridges that promote rapid intercontinental spread of the wheat stem rust pathogen

“…From its initial detection in Uganda in 1998, Ug99 race TTKSK took five years before detection in Ethiopia, eight years before detection in Yemen, and nine years before detection in Iran (see table 1 in Singh et al 2015). In contrast, since being first detected in Kenya in 2014 (Patpour et al 2016), and Ethiopia in 2018 (Hei et al 2020), race TTKTT was detected in Iraq in 2019, just one year later (Nazari et al 2021). Race TTKTT is now the second Ug99 variant to move into the Middle East, indicating a possible common migration route.…”

Characterisation of a major adult plant resistance gene in the South African winter wheat cultivar PAN 3161

“…Pgt races in the Ug99 group are virulent to many race-speci c stem rust (Sr) resistance genes including Sr24, Sr31, Sr36 and Sr38 that are prevalent in common wheat worldwide (Pretorius et al 2000;Jin et al 2007Jin et al , 2009Singh et al 2008Singh et al , 2011aFetch et al 2021). Ug99 has evolved since its rst detection in Uganda in 1998 (Pretorius et al 2000); 15 variants have been detected in 14 African and Asian countries (Nazari et al 2021; https://rusttracker.cimmyt.org/?page_id=22).…”