Race analysis of Puccinia graminis f. sp. tritici led to identification of the new race TTKTK, affecting Sr31 and SrTmp, in Iran

The basidiomycetous fungus, Puccinia graminis f. sp. tritici (Pgt) causes stem rust disease as one of the most destructive wheat pathogens, worldwide. TTKSK and other Pgt races under Ug99 race group are considered as major threats to wheat production in east Africa and CWANA region by defeating the stem rust resistance gene Sr31, while its ineffectiveness was reported in Iran in 2007. Race TKTTF of Pgt caused a severe stem rust epidemic in southern Ethiopia in 2013, and was spread to Europe through 2016 Sicily outbreak. This research describes race identification of Iranian isolates collected during the widespread distribution of stem rust in 2014-16. Purified urediniospores of 123 Pgt isolates were separately inoculated on seedlings of 20 North American differential wheat cultivars carrying different Sr resistance gene/s. Infection types were recorded at 14 days post inoculation (dpi) using Stakman et al. 0-4 scale. Based on the letter code nomenclature, we identified the Pgt races TKTTF, TTTTF, TTKSK, TTKTK, PKTTF, TKSTF, PKSTF, PKTTC, PTRTF, PTTTF, PKSTC, TTRTF, TKSTC and PKRTF in Iran. TKTTF and TTTTF were determined as prevalent Iranian Pgt races. This is the first report of race TTKTK, a new variant of Ug99 race group with virulence on Sr31 and SrTmp resistance genes, in Iran. Since TTKTK primarily occurred in south west of Iran, the migration route for this new race seems to be similar to race TTKSK. The high race variation observed in this study could indicate a high genetic diversity among P. graminis f. sp. tritici populations in Iran, as a wheat center of origin.