Detection of Virulence to Resistance Gene Sr24 Within Race TTKS of Puccinia graminis f. sp. tritici.

01/2008; DOI: 10.1094/PDIS-92-6-0923
Source: OAI

ABSTRACT 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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    ABSTRACT: North American durum lines, selected for resistance to TTKSK (Ug99) and related races of Puccinia graminis f. sp. tritici in Kenya, became susceptible in Debre Zeit, Ethiopia, suggesting the presence of stem rust races that were virulent to the TTKSK-effective genes in durum. The objective of this study was to characterize races of P. graminis f.sp. tritici present in the Debre Zeit, Ethiopia stem rust nursery. Three races of P. graminis f. sp. tritici were identified from 34 isolates:JRCQC, TRTTF, and TTKSK. Both races JRCQC and TRTTF possess virulence on stem rust resistance genes Sr13 and Sr9e, which may explain why many TTKSK-resistant durum lines tested in Kenya became susceptible in Debre Zeit. The Sr9e-Sr13 virulence combination is of particular concern because these two genes constitute major components of stem rust resistance in North American durum cultivars. In addition to Sr9e and Sr13 virulence, race TRTTF is virulent to at least three stem rust resistance genes that are effective to race TTKSK,including Sr36, SrTmp, and resistance conferred by the 1AL.1RS rye translocation. Race TRTTF is the first known race with virulence to the stem rust resistance carried by the 1AL.1RS translocation, which represents one of the few effective genes against TTKSK in winter wheat cultivars in the United States. Durum entries exhibiting resistant to moderately susceptible infection response at the Debre Zeit nursery in 2009 were evaluated for reaction to races JRCQC, TRTTF, and TTKSK at the seedling stage. In all, 47 entries were resistant to the three races evaluated at the seedling stage, whereas 26 entries exhibited a susceptible reaction. These results suggest the presence of both major and adult plant resistance genes, which would be useful in durum wheat-breeding programs. A thorough survey of virulence in the population of P. graminis f. sp. tritici in Ethiopia will allow characterization of the geographic distribution of the races identified in the Debre Zeit field nursery.
    Plant Disease 01/2012; 96:623-628. · 2.74 Impact Factor
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    ABSTRACT: Stem rust, caused by Puccinia graminis, is an important disease of cereal crops that is primarily controlled in Canada through cultivar resistance. Surveys of common barley (Hordeum vulgare), common oat (Avena sativa), and common wheat (Triticum aestivum) fields and trap nurseries were conducted to obtain incidence and severity information and to identify changes in virulence structure in the pathogen populations. Stem rust samples were collected in Saskatchewan, Manitoba, and Quebec in 2005. Stem rust was not found on cultivated wheat and was at trace levels in barley and oat fields. For the first time since surveys started in 1919, only one race (QFCSC) of P. graminis f. sp. tritici was found on wheat or barley in Canada. Eleven races of P. graminis f. sp. avenae were found in 2005. The predominant races from cultivated oat samples from Saskatchewan and Manitoba were TJJ (33% and 57%, respectively), TGB (39% and 12%), TJG (11% and 21%), and TGD (17% and 6%). The predominant races from wild oat samples from Saskatchewan and Manitoba were TGB (49% and 31%, respectively), TJJ (15% and 30%), TGD (12% and 25%), and TJD (17% and 4%). In Quebec, three races (CDJ, FDJ, and TDD) distinct from those in the Prairie region were found. Additionally, a new race of P. graminis f. sp. avenae (TJS) with virulence on the Pg-a resistance-gene complex and all single-gene differential lines except Pg6, Pg10, Pg11, and Pg16 was detected in Manitoba in 2005. Résumé : Au Canada, la rouille des tiges, causée par Puccinia graminis, est une maladie courante chez les céréales. Celle-ci est tenue en échec grâce à la résistance des cultivars. Des études effectuées dans des champs et des pépinières à parcelles pièges ont été menées sur l'orge (Hordeum vulgare), l'avoine (Avena sativa) et le blé (Triticum aestivum) afin de fournir de l'information sur l'incidence et la gravité de la maladie ainsi que pour caractériser les changements se produisant dans la structure de la virulence chez les populations d'agents pathogènes. En 2005, des échantillons de rouille des tiges ont été collectés en Saskatchewan, au Manitoba et au Québec. Il n'y avait à proprement dit pas de rouille des tiges dans les champs de blé et que des traces sur l'orge et l'avoine cultivées en champs. Pour la première fois depuis que les études on débuté, en 1919, une seule race (QFCSC) de P. graminis f. sp. tritici était détectée sur le blé ou l'orge au Canada. Par ailleurs, 11 races de P. graminis f. sp. avenae ont été trouvées en 2005. Chez les échantillons d'avoine cultivée, les races suivantes prédominaient en Saskatchewan et au Manitoba : TJJ (33 % et 57 %, respectivement), TGB (39 % et 12 %), TJG (11 % et 21 %) et TGD (17 % et 6 %). Chez les échantillons de folle avoine, les races suivantes prédominaient en Saskatchewan et au Manitoba : TGB (49 % et 31 %, respectivement), TJJ (15 % et 30 %), TGD (12 % et 25 %) et TJD (17 % et 6 %). Au Québec, on a trouvé trois races différentes de celles des Prairies canadiennes : CDJ, FDJ et TDD. De plus, une nouvelle race de P. graminis f. sp. avenae (TJS), virulente envers le complexe du gène Pg-a et envers toutes les lignées différentielles à gène simple, sauf Pg6, Pg10, Pg11 et Pg16, a été détectée au Manitoba en 2005. Mots-clés : orge, avoine, rouille des tiges, virulence, phénotype de virulence, blé. Fetch: Puccinia graminis / barley, oat, and wheat / races / 2005 survey 79
    Canadian Journal of Plant Pathology 01/2009; 31:74-79. · 1.12 Impact Factor

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