First report of TTRTF race of the wheat stem rust pathogen, Puccinia graminis f. sp. tritici from Iran (Northwest, Cold Zone)

Stem rust or black rust of wheat caused by Puccinia graminis f. sp. tritici (Pgt) is one of the most important and devastating wheat diseases, worldwide. Pgt possesses a high potential of genetic recombination through sexual reproduction on intermediate host which could lead to the production of new races with various virulence patterns. TTRTF, one of the novel and virulent races of Pgt, has been present in Georgia, USA since 2014; however, it was officially reported in 2016 following a widespread outbreak of stem rust on durum wheat in Sicily, Italy (Patpour et al. 2018). This race was observed in Egypt in 2016, and reported from Hungry, Egypt and Eritrea in 2017, 2018 and 2020, respectively (Patpour et al. 2020). In this study, 150 stem rust samples were collected from infected wheat fields in different regions of Iran during 2014 to 2019. Race analysis of single-pustuled isolates was carried out using 20 North American differential wheat genotypes (obtained from CIMMYT) as well as a set of 45 supplementary differential genotypes (obtained from ICARDA) based on Jin et al. (2008) method. Infection types of differential genotypes were recorded based on modified 0-4 scale of McIntosh et al. (1995) at 14 dpi. Results revealed high pathotypic (race) diversity among collected Pgt isolates. Race analysis of isolates from Oshnavieh region, West Azerbaijan province led to identification of the race TTRTF from northwest of Iran. Inoculation of wheat genotypes carrying the resistance genes Sr5, Sr6, Sr7a, Sr7b, Sr8a, Sr8b, Sr9a, Sr9b, Sr9d, Sr9e, Sr9g, Sr10, Sr11, Sr12, Sr13, Sr14, Sr15, Sr16, Sr17, Sr18, Sr19, Sr20, Sr21, Sr23, Sr28, Sr29, Sr34, Sr35, Sr36, Sr37, Sr38, SrTmp < /em> and SrMcn revealed susceptible reaction to TTRTF. Contrarily, wheat genotypes carrying the resistance genes Sr22, Sr24, Sr25, Sr26, Sr27, Sr30, Sr31, Sr32, Sr33, Sr39 and Sr40 were evaluated as resistant to this race. However, reaction of genotypes carrying the genes Sr44, Sr45, and Sr50 (adult plant resistance genes) to TTRTF race of Pgt has been reported as susceptible (Patpour et al. 2020). Some of the Sr resistance genes that displayed effectiveness against many Iranian P. graminis f. sp. tritici races are ineffective to this race. Due to new virulence pattern, this race is assumed as a serious threat to global food security, particularly in rust suitable areas including Iran. Identification of effective sources of resistance to TTRTF, and exploiting them in wheat breeding programs could be considered as one of the main strategies in stem rust management.