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ARS Home » Midwest Area » St. Paul, Minnesota » Cereal Disease Lab » Research » Publications at this Location » Publication #219756
Title: Detection of Virulence to Resistance Gene Sr24 within Race TTKS of Puccinia graminis f. sp. tritici

Author
item Jin, Yue
item Szabo, Les
item PRETORIOUS, Z. - UNIV.FREE STATE,AFRICA
item SINGH, R. - CIMMYT, MEXICO
item FETCH, JR., T. - AGRI-FOOD, CANADA

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/7/2008
Publication Date: 6/1/2008
Citation: Jin, Y., Szabo, L.J., Pretorious, Z., Singh, R., Fetch, Jr., T. 2008. Detection of Virulence to Resistance Gene Sr24 within Race TTKS of Puccinia graminis f. sp. tritici. Plant Disease. 92:923-926.

Interpretive Summary: Wheat stem rust is an important disease of wheat. The stem rust resistance gene Sr24 is effective against most races of Puccinia graminis f. sp. tritici, including race TTKS (syn. Ug99), and utilized widely in commercial wheat cultivars worldwide. In 2006, susceptible type of infection were observed on wheat lines and cultivars carrying Sr24 in a field stem rust screening nursery at Njoro, Kenya. We investigated the infection by testing samples on wheat stem rust differential lines and determined that field susceptible reaction on Sr24 represented a new variant of race TTKS with virulence to Sr24. DNA markers were used to to examine the genetic relationship between 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 simple sequence repeat (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 has likely arisen via mutation within the TTKS genetic lineage. We propose to revise the North American stem rust nomenclature system by 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.

Technical Abstract: The stem rust resistance gene Sr24 is effective against most races of Puccinia graminis f. sp. tritici, including race TTKS (syn. Ug99), and utilized 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 stem rust differential lines and on wheat lines carrying Sr24, Sr31, Sr38, SrMcN, and a combination of Sr24 and Sr31. All isolates were identified as race TTKS with virulence on Sr31 and Sr38. These isolates were divided into two groups, group A (nine isolates) producing a low infection type and group B (19 isolates) produced 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 simple sequence repeat (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 has likely arisen via mutation within the TTKS genetic lineage. We propose to revise the North American stem rust nomenclature system by 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.