Races of Puccinia graminis f. sp. tritici with virulence on Sr13 and Sr9e in durum screening nursery in Ethiopia

Durum wheat (Triticum turgidum ssp. durum) of North America has a higher frequency of resistance to race TTKSK (or Ug99) of Puccinia graminis f. sp. tritici than common wheat based on evaluations conducted in Njoro, Kenya. We postulated TTKSK resistance in durum is likely due to Sr13, a common gene in North American cultivars. However, when resistant selections were evaluated in Debre Zeit, Ethiopia, many became susceptible to stem rust, suggesting that local races may possess a virulence combination that overcomes the TTKSK resistance. The objective of this study was to identify and characterize races of P. graminis f. sp. tritici present in the Debre Zeit screening nursery in 2009. Single-pustule isolates were derived from collected samples and race-typed based on the North American stem rust differentials. The isolates were further characterized on a set of universal resistant lines. Three races of P. graminis f. sp. tritici were identified: JRCQC, TRTTF and TTKSK. Both JRCQC and TRTTF possess virulence combination on Sr13 and Sr9e, which may explain why the TTKSK-resistant durum in Kenya became susceptible in Debre Zeit. The virulence combination on Sr9e and Sr13 is of big concern because these genes constitute the main components of stem rust resistance in North American durum cultivars. In addition to virulence on Sr9e and Sr13, race TRTTF appears to be virulent to stem rust resistance conferred by the 1AL.1RS translocation in winter wheat in the United States.