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      Races of Puccinia graminis f. sp. tritici with Combined Virulence to Sr13 and Sr9e in a Field Stem Rust Screening Nursery in Ethiopia

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      Plant Disease
      Scientific Societies

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          The emergence of Ug99 races of the stem rust fungus is a threat to world wheat production.

          Race Ug99 of the fungus Puccinia graminis tritici that causes stem or black rust disease on wheat was first detected in Uganda in 1998. Seven races belonging to the Ug99 lineage are now known and have spread to various wheat-growing countries in the eastern African highlands, as well as Zimbabwe, South Africa, Sudan, Yemen, and Iran. Because of the susceptibility of 90% of the wheat varieties grown worldwide, the Ug99 group of races was recognized as a major threat to wheat production and food security. Its spread, either wind-mediated or human-aided, to other countries in Africa, Asia, and beyond is evident. Screening in Kenya and Ethiopia has identified a low frequency of resistant wheat varieties and breeding materials. Identification and transfer of new sources of race-specific resistance from various wheat relatives is underway to enhance the diversity of resistance. Although new Ug99-resistant varieties that yield more than current popular varieties are being released and promoted, major efforts are required to displace current Ug99 susceptible varieties with varieties that have diverse race-specific or durable resistance and mitigate the Ug99 threat. Copyright © 2011 by Annual Reviews. All rights reserved.
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            Detection of Virulence to Resistance GeneSr24Within Race TTKS ofPuccinia graminisf. sp.tritici

            The stem rust resistance gene Sr24 is effective against most races of Puccinia graminis f. sp. tritici, including race TTKS (syn. Ug99), and is used widely in commercial wheat cultivars worldwide. In 2006, susceptible infection responses were observed on wheat lines and cultivars carrying Sr24 in a field stem rust screening nursery at Njoro, Kenya. We derived 28 single-pustule isolates from stem rust samples collected from the 2006 Njoro nursery. The isolates were evaluated for virulence on 16 North American stem rust differential lines; on wheat lines carrying Sr24, Sr31, Sr38, and SrMcN; and on a wheat cultivar with a combination of Sr24 and Sr31. All isolates were identified as race TTKS with additional virulence on Sr31 and Sr38. These isolates were divided into two groups: group A (seven isolates and the two control isolates), producing a low infection type, and group B (21 isolates), producing a high infection type on Sr24, respectively. Isolates of group B represented a new variant of race TTKS with virulence to Sr24. Eighteen simple sequence repeat (SSR) markers were used to examine the genetic relationship between these two groups of isolates in race TTKS and five North American races (MCCF, QCCQ, RCRS, RTHS, and TPMK) that are representative of distinct lineage groups. All isolates of race TTKS shared an identical SSR genotype and were clearly different from North American races. The virulence and SSR data indicated that the new variant of race TTKS with Sr24 virulence likely has arisen via mutation within the TTKS genetic lineage. We propose to revise the North American stem rust nomenclature system by the addition of four genes (Sr24, Sr31, Sr38, and SrMcN) as the fifth set. This revision recognizes the virulence on Sr31 and differentiates isolates within race TTKS into two separate races: TTKSK and TTKST, with avirulence and virulence on Sr24, respectively. The occurrence of race TTKST with combined virulence on Sr24 and Sr31 has substantially increased the vulnerability of wheat to stem rust worldwide.
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              Characterization of Seedling Infection Types and Adult Plant Infection Responses of Monogenic Sr Gene Lines to Race TTKS of Puccinia graminis f. sp. tritici

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                Author and article information

                Journal
                Plant Disease
                Plant Disease
                Scientific Societies
                0191-2917
                May 2012
                May 2012
                : 96
                : 5
                : 623-628
                Article
                10.1094/PDIS-09-11-0793
                30727519
                f92f2d88-6813-4416-b582-2facbe7956b9
                © 2012
                History

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