Wheat stem rust back in Europe: Diversity, prevalence and impact on host resistance

Authors: PATPOUR, MEHRAN - Aarhus University; HOVMØLLER, MOGENS - Aarhus University; RODRIGUEZ-ALGABA, JULIAN - Aarhus University; RANDAZZO, BIAGIO - University Of Palermo Italy; VILLEGAS, DOLORS - Institute De Recerca I Tecnologia Agroalimentaries (IRTA); SHAMANIN, VLADIMIR - Omsk State Agrarian University; BERLIN, ANNA - Swedish University Of Agricultural Sciences; FLATH, KERSTIN - Julius Kuhn Institute; CZEMBOR, PAWEL - Plant Breeding And Acclimatization Institute (IHAR); HANZALOVA, ALENA - Crop Research Institute - Czech Republic; SLIKOVÁ, SVETLANA - Omsk State Agrarian University; SKOLOTNEVA, EKATERINA - Russian Academy Of Sciences; Jin, Yue; Szabo, Les; MEYER, KEVIN - Inrae; VALADE, ROMAIN - Arvalis Plant Institute; THACH, T - Aarhus University; HANSEN, J - Aarhus University; JUSTESEN, ANNEMARIE - Aarhus University

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2022
Publication Date: 6/2/2022
Citation: Patpour, M., Hovmøller, M.S., Rodriguez-Algaba, J., Randazzo, B., Villegas, D., Shamanin, V.P., Berlin, A., Flath, K., Czembor, P., Hanzalova, A., Sliková, S., Skolotneva, E.S., Jin, Y., Szabo, L.J., Meyer, K.J., Valade, R., Thach, T., Hansen, J.G., Justesen, A.F. 2022. Wheat stem rust back in Europe: Diversity, prevalence and impact on host resistance. Frontiers in Plant Science. 13. Article 882440. https://doi.org/10.3389/fpls.2022.882440.
DOI: https://doi.org/10.3389/fpls.2022.882440

Interpretive Summary: Stem rust, caused by the fungal pathogen Puccinia graminis f. sp. tritici, is an important disease of wheat. The disease has become increasingly prevalent in Europe since 2016, with epidemic levels on both durum and bread wheat in local areas in southern Europe, and sporadic outbreaks in new areas in central/western Europe. Analyses of stem rust samples identified genotypes that belong to several major lineages that have been detected previously in Europe and elsewhere. In contrast, huge diversity with respect to virulence and genotypes have been detected in local populations in Spain and Sweden that were associated with the alternate host Berberis spp. The presence of Sr31-virulence in multiple and highly diverse races in local populations in Spain, and in one case in a population from Siberia, stress that virulence may emerge independent and multiple times when large geographical areas and time spans are considered, and that Sr31-virulence is not unique to Ug99. Tests of representative European wheat varieties with these prevalent races revealed that a high proportion of European wheat varieties were susceptible to stem rust. The study included comprehensive efforts for the alignment of SNP and SSR based genotyping results from different laboratories, as well as race phenotyping, which allowed us to connect results from the present study with previous European and international studies of wheat stem rust. Our results suggest that the alternate host for Puccinia graminis, Berberis spp., has returned as an important component in the epidemiology of wheat stem rust in Europe. In addition, breeding efforts to increase stem rust resistance in European wheat germplasm is strongly recommended. This research will be highly useful for scientists and specialists to develop strategies in disease management.

Technical Abstract: Puccinia graminis f.sp. tritici has become increasingly prevalent in Europe since 2016, with epidemic levels on both durum wheat and bread wheat in local areas in southern Europe, and sporadic outbreaks in new areas in central/western Europe. Three distinct genotypes/races were prevalent in many areas, Clade III-B (TTRTF), Clade IV-B (TKTTF), and Clade IV-F (TKKTF). None of these have been detected in Europe prior to 2016. A fourth group, termed Clade VIII, first detected in Germany (2013), was observed in several years in Central/East Europe. Tests of representative European wheat varieties with these prevalent races revealed that a high proportion of European wheat varieties were susceptible to stem rust. In contrast, huge diversity with respect to virulence and Simple Sequence Repeat (SSR) markes were detected in local populations on cereals/grasses in proximity to Berberis spp in Spain and Sweden. Reference populations from Omsk and Novosibirsk in western Siberia also revealed huge genetic diversity, but clearly different from European populations. The presence of Sr31-virulence in multiple and highly diverse races in local populations in Spain, and in one case in a population from Siberia, stress that virulence may emerge independent and multiple times when large geographical areas and time spans are considered and that Sr31-virulence is not unique to Ug99. The fact that wheat, rye and grass species were susceptible to these genetically diverse, local populations in Spain may suggest that host barriers within Puccinia graminis, previously used to define formae speciales, should be explored in more detail. The study included comprehensive efforts for the alignment of SNP and SSR based genotyping results from different laboratories, as well as race phenotyping, which allowed us to connect results from the present study with previous European and international studies of wheat stem rust. Our results suggest that the alternate host for Puccinia graminis, Berberis spp., has returned as an important component in the epidemiology of wheat stem rust in Europe. In addition, breeding efforts to increase stem rust resistance in European wheat germplasm is strongly recommended.