A unique race of the wheat stem rust pathogen with virulence on Sr31 identified in Spain and reaction of wheat and durum cultivars to this race

Authors: OLIVERA, PABLO - University Of Minnesota; VILLEGAS, DOLORS - Universitat De Lleida; CANTERO-MARTINEZ, CARLOS - Universitat De Lleida; Szabo, Les; Rouse, Matthew; Luster, Douglas - Doug; BARTAULA, RADHIKA - University Of Minnesota; LOPES, MARTA - Universitat De Lleida; Jin, Yue

Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/14/2022
Publication Date: 1/28/2022
Citation: Olivera, P.D., Villegas, D., Cantero-Martinez, C., Szabo, L.J., Rouse, M.N., Luster, D.G., Bartaula, R., Lopes, M.S., Jin, Y. 2022. A unique race of the wheat stem rust pathogen with virulence on Sr31 identified in Spain and reaction of wheat and durum cultivars to this race. Plant Pathology. 71(4):873-889. https://doi.org/10.1111/ppa.13530.
DOI: https://doi.org/10.1111/ppa.13530

Interpretive Summary: Wheat stem rust, caused by the fungal pathogen Puccinia graminis f. sp. tritici, is a re-emerging disease. Stem rust outbreaks are occurring in many wheat-growing regions in the world. We are a part of the global stem rust surveillance network to detect potential new virulences that may pose a threat to wheat production worldwide. We analyzed stem rust samples collected in 2018 from two locations in Spain. Two virulent types (or races) were identified: one is called race TKTTF from Cadiz Province and the other one is called race TKHBK from Teruel Province. Race TKTTF has a wide distribution across Europe and other important wheat growing regions in the world. Race TKHBK, which derived from a sample collected in a wheat field adjacent to barberry bushes, has a unique virulence combination that includes virulence to Sr31, a stem rust resistance gene widely used in breeding worldwide. Race TKHBK is the first race outside the Ug99 race group with virulence to Sr31 and the first known race with virulence to a newly identified resistance gene Sr59. Race TKHBK is unique, not related to previously described genetic groups. We tested bread and durum wheat germplasm from Spain to these races and identified resistance. Resistant cultivars identified in this study may be used to improve and diversify stem rust resistance. This research will be useful for scientists involved in wheat breeding and pathogen surveillance.

Technical Abstract: Wheat stem rust, caused by Puccinia graminis f. sp. tritici, is a re-emerging disease, posing a threat to wheat production. In Spain, stem rust has not been detected since 1970s, but infection was observed in wheat fields in 2018. We analyzed six stem rust samples collected in Rota, Cadiz province and one from Monteagudo del Castillo, Teruel province. All the samples from Rota were typed as race TKTTF, whereas the sample from Monteagudo del Castillo, collected in a wheat field adjacent to barberry bushes, was typed as race TKHBK. This race has a unique and significant virulence combination that includes virulence to Sr31, Sr33, Sr53 and Sr59, and is avirulent to Rusty, a durum line developed for universal susceptibility to the wheat stem rust pathogen. TKHBK is the first race outside the Ug99 race group with virulence to Sr31 and the first known race with virulence to Sr59. Genotyping studies indicate that race TKHBK does not belong to the Ug99 or TKTTF race groups and constitutes a previously unknown lineage. Two hundred bread and durum wheat cultivars and breeding lines from Spain were evaluated against TKHBK and TKTTF and six additional races. Resistance was observed to all the races evaluated. Molecular markers confirmed the presence of Sr38, Sr31, Sr24, Sr7a, and Sr57 in bread wheat, and Sr13 in durum wheat. The re-emergence of wheat stem rust in Spain and the occurrence of unique virulences underscore the need to continue surveying and monitoring this disease.