Puccinia graminis f.sp. tritici population causing recent wheat stem rust epidemics in Kazakhstan is highly diverse and includes novel virulence pathotypes

Authors: OLIVERA, PABLO - University Of Minnesota; Szabo, Les; KOKHMETOVA, ALMA - Institute Of Plant Biology And Biotechnology; MORGOUNOV, ALEX - International Maize & Wheat Improvement Center (CIMMYT); Luster, Douglas - Doug; Jin, Yue

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/25/2022
Publication Date: 11/30/2023
Citation: Olivera, P.D., Szabo, L.J., Kokhmetova, A., Morgounov, A., Luster, D.G., Jin, Y. 2023. Puccinia graminis f.sp. tritici population causing recent wheat stem rust epidemics in Kazakhstan is highly diverse and includes novel virulence pathotypes. Phytopathology. 112(11):2403-2415. https://doi.org/10.1094/PHYTO-08-21-0320-R.
DOI: https://doi.org/10.1094/PHYTO-08-21-0320-R

Interpretive Summary: Wheat stem rust, caused by fungal pathogen Puccinia graminis f. sp. tritici, is one of the most important wheat diseases that can cause complete crop failure. Severe stem rust epidemics in northern Kazakhstan and western Siberia have occurred in the period of 2015-2019. We analyzed 51 stem rust samples collected between 2015 and 2017 in five regions in Kazakhstan in order to understand the pathogen races that have caused these epidemics. A large number of races or strains (112 in total) were identified. These isolates are phenotypically and genotypically diverse and most of them are likely derived from the sexual cycle of the pathogen. Pathogen isolates from Akmola and North Kazakhstan regions were genetically similar, indicating that the northern regions of the country consisted of a single pathogen population. In addition to the strains of sexual origin, six strains reported previously in Europe, the Caucasus and East Africa were detected in Kazakhstan, indicating that this epidemiological region is not isolated, and spore movement from the west occurs. Virulences alone or in combination to several important resistance genes, including genes effective against the Ug99 race group, were detected, including novel virulence on Sr32+Sr40 and Sr47. The occurrence of a highly diverse pathogen population with virulence to important stem rust resistance genes is indicative of the importance of sexual cycle in generating new and significant virulence combinations that can overcome the resistance genes being used in wheat breeding for rust resistance. This research provided basis for improving disease management strategies including combining multiple effective genes in breeding programs as well as eliminating the roles of the alternate host in pathogen variations and disease epidemiology. This research will be very useful for researchers in global surveillance of important plant pathogens, disease management, and for breeders in wheat improvement for rust resistance.

Technical Abstract: Wheat stem rust, caused by Puccinia graminis f. sp. tritici (Pgt), is a re-emerging disease, causing severe epidemics in northern Kazakhstan and western Siberia in the period of 2015-2019. We analyzed 51 stem rust samples collected between 2015 and 2017 in five regions in Kazakhstan. A total of 112 Pgt races were identified from 208 single-pustule isolates. These races are phenotypically and genotypically diverse and most of them are likely of sexual origin. No differentiation of phenotypes and SNP genotypes was observed between isolates from Akmola and North Kazakhstan regions supporting the idea of a wide dispersal of inoculum in the northern regions of the country. Similarities in virulence profiles with Pgt races previously reported in Siberia, Russia suggest that northern Kazakhstan and western Siberia constitute a single stem rust epidemiological region. In addition to the races of sexual origin, six races reported in Europe, the Caucasus, and East Africa were detected in Kazakhstan, indicating that this epidemiological region is not isolated, and spore inflow from the west occurs. Virulences alone or in combination to several genes effective against the Ug99 race group were detected, including novel virulence on Sr32+Sr40 and Sr47. The occurrence of a highly diverse Pgt population with virulence to an important group of Sr genes demonstrated the importance of the pathogen’s sexual cycle in generating new and significant virulence combinations.