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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.
Stem rust is a potentially destructive fungal disease of wheat worldwide. In 1998 Pgt pathotype TTKSK virulent to Sr31 was detected in Uganda. The same pathotype was confirmed in Lorestan and Hamedan provinces of Iran in 2007. We used a derivative of race TTKSK to phenotype 62 Iranian wheat landraces (resistant to stripe rust in a previous study) at the seedling stage to this new pathotype (TTSSK). Twenty eight accessions were evaluated for the presence of resistance genes Sr2, Sr22, Sr24, Sr25, Sr26, Sr35, Sr36 and Srweb using SSR markers. None carried Sr2, Sr24 or Sr26, but the presence of Sr22, Sr25, Sr35 and Sr36 was indicated. Some susceptible landraces predicted to carry Sr2 by marker analysis require further investigation. To evaluate defense gene expression in compatible and incompatible stem rust interactions we sampled resistant and susceptible cultivars at 0, 12, 18, 24, 72 hours post-inoculation (hpi). ?-1,3 glucanase expression was studied using qGLU-S and qGLUU-AS primers and a real-time PCR step-one ABI machine, with ?-tubulin and EF1-? genes used as internal controls. In incompatible interactions defense gene expression was increased at 24 hpi, but in compatible interactions the highest level of expression occurred at 12 hpi and was significantly decreased at 18 hpi. The results revealed that expression of defense genes such as ?-1,3 glucanase was earlier in compatible than in incompatible interactions but the expression level was less in incompatible interactions. On the other hand, in susceptible genotypes the expression of defense genes increased immediately after inoculation and declined sharply after infection. In contrast defense gene expression in resistant genotypes began to increase after establishment of the pathogen.
Stem (black) rust is a potentially important disease in northern, western and southern Iran. A new Pgt race with virulence to gene Sr31 appeared in Iran in 2007. Similar races have spread in Africa and some CWANA countries. In 2014 stem rust was widespread in western, northern, northwestern and central Iran, but at low severities. Thirty-nine stem rust samples were collected for race analysis. After purification and increase each isolate was inoculated to a set of 20 North American differentials in the greenhouse. Infection types were recorded 12-14 days after inoculation using the scale described by McIntosh et al. (1995, Wheat Rusts: An Atlas of Resistance Genes, CSIRO, East Melbourne, Australia). Races TKSTC (59%), TKTTC (20%), TTTTC, KTTSK (virulent on plants with Sr31), TTSTC, PTTTF and TTTTF were detected. Race TKSTC was common in western, northwestern and central Iran. Except for avirulence to Sr17 this race is similar to the race (TKTT) that caused a stem rust epidemic in Ethiopia in 2013.
Resistance is an effective and economic method of controlling wheat stem rust provided the resistance gene(s) remains effective. We studied the stem rust responses of 372 synthetic hexaploid wheats (SHW) originally from CIMMYT under natural field infection conditions at Kelardasht, a stem rust hotspot. Stem rust severities were recorded using the modified Cobb scale prior to harvest ripeness. Seventy six and 17% of the genotypes (93% in total) were scored susceptible or moderately susceptible, whereas only 5 and 2% (7% in total) were moderately resistant or resistant, respectively. Based on our results, 26% of the genotypes were considered to have resistance, displaying field responses of 40MS to 20MSS. Those SHWs resistant to local Pgt races at Kelardasht could be used as sources of resistance in Iranian wheat breeding programs. Race analysis of Pgt isolates from the trials and seedling response tests on the entire SHW set are in progress.