ARS | Publication request: Detection of Virulence to Resistance Gene Sr36 within Race TTKS Lineage of Puccinia graminis f. sp. tritici

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 10, 2008
Publication Date: April 1, 2009
Repository URL: http://hdl.handle.net/10113/32222
Citation: Jin, Y., Szabo, L.J., Rouse, M., Fetch, T., Pretorious, Z., Wanyera, R., Njau, P. 2009. Detection of Virulence to Resistance Gene Sr36 within Race TTKS Lineage of Puccinia graminis f. sp. tritici. Plant Disease. 93:367-370.

Interpretive Summary: Wheat stem rust is an important disease of wheat. The stem rust resistance gene Sr36 is highly effective against race TTKS (syn. Ug99) of the stem rust pathogen, thus considered an important source of resistance for breeding resistance to this virulent race. This gene occurs in a high frequency in the US soft winter wheat germplasm. In 2007, susceptible types of infection were observed on wheat lines and cultivars carrying Sr36 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 Sr36 was due to race TTTSK, representing a new variant within the TTKS lineage with virulence to Sr36. DNA markers were used to examine the genetic relationship between isolates in the TTKS lineage. All isolates of race TTKS shared an identical simple sequence repeat (SSR) genotype. Wheat cultivars and breeding lines postulated to possess Sr36 became susceptible to TTTKS. The occurrence of race TTTSK with combined virulence on Sr31 and Sr36 has further broadened the virulence spectrum of the TTKS lineage and rendered an important source of resistance ineffective.

Technical Abstract: The stem rust resistance gene Sr36 is highly effective against race TTKS (syn. Ug99) of Puccinia graminis f. sp. tritici, conferring near immunity to TTKS that possesses unusually broad virulence combinations. Because of this gene is widely spread in the adapted US soft winter wheat breeding germplasm and cultivars, it has been considered as an important source of resistance to TTKS in breeding. In 2007, moderately susceptible infection responses were observed on wheat lines and cultivars carrying Sr36 in a field stem rust screening nursery at Njoro, Kenya. We derived 10 single-pustule isolates from stem rust samples collected from the 2007 Njoro nursery. The isolates were evaluated for virulence on 20 North American stem rust differential lines and on wheat lines and cultivars carrying Sr36, Sr31+Sr36, Sr24+Sr31. All isolates were identified as race TTTSK with virulence to Sr36. Race TTTKS represented a new variant within the TTKS lineage. Races TTKSK and TTKST, avirulent and virulent to Sr24, respectively, were also identified. Eighteen simple sequence repeat (SSR) markers were used to examine the genetic relationship between the three races in the TTKS lineage. All isolates in the lineage shared an identical simple sequence repeat (SSR) genotype and were clearly different from North American races. Sixteen wheat cultivars and 60 elite breeding lines, postulated to possess Sr36, became susceptible to race TTTSK. The occurrence of race TTTSK with combined virulence on Sr31 and Sr36 has further broadened the virulence spectrum of the TTKS lineage and rendered an important source of resistance ineffective.