Virulence of Blumeria graminis f.sp. tritici in Brazil, South Africa, Turkey, Russia and Australia

Authors: KLOPPE, TIM - North Carolina State University; BOSHOFF, WILLEM - University Of The Free State; PRETORIUS, ZACHARIAS - University Of The Free State; LESCH, DRIECUS - Syngenta - South Africa; AKIN, BEYHAN - International Maize & Wheat Improvement Center (CIMMYT); MORGOUNOV, ALEXEY - Food And Agriculture Organization Of The United Nations; SHAMANIN, VLADIMIR - Omsk State Agrarian University; KUHNEM, PAULO - Biotrigo Genetica, Ltda; MURPHY, PAUL - North Carolina State University; Cowger, Christina

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/20/2022
Publication Date: 8/1/2022
Citation: Kloppe, T., Boshoff, W., Pretorius, Z., Lesch, D., Akin, B., Morgounov, A., Shamanin, V., Kuhnem, P., Murphy, P., Cowger, C. 2022. Virulence of Blumeria graminis f.sp. tritici in Brazil, South Africa, Turkey, Russia and Australia. Frontiers in Plant Science. 10:3389. https://doi.org/10.3389/fpls.2022.954958.
DOI: https://doi.org/10.3389/fpls.2022.954958

Interpretive Summary: The fungus Blumeria graminis f. sp. tritici (Bgt) causes wheat powdery mildew, a disease that causes losses in wheat production in many countries around the world. Bgt can adapt to control measures such as wheat resistance very quickly, so surveys are important to check whether the fungus is in the process of overcoming resistance genes(Pm genes) that are used in commercial wheat breeding programs. We tested a total of 346 Bgt isolates (samples) from 5 countries that had either recently experienced increasing powdery mildew epidemics (Brazil, South Africa and Australia) or had not recently been surveyed for Pm gene effectiveness (Turkey and Russia). Then we compared our results to surveys of U.S. and Egyptian Bgt previously conducted in our lab (390 isolates). Many of the Pm genes that may have been used for a longer time in wheat breeding (Pm1a – Pm17) were shown to have lost effectiveness. Bgt isolates from Brazil were able to overcome more of those Pm genes than isolates from any other country. Australian isolates were able to overcome Pm1a, probably because a wheat variety called Wyalkatchem that contains Pm1a had been planted widely there. We also tested a set of Pm genes that were recently brought from wild wheat relatives into winter bread wheat, although they have not yet been widely used in commercial varieties. The Bgt isolates from the Fertile Crescent countries of Egypt and Turkey stood out for their generally moderate ability to cause disease when confronted with both the older and newer Pm genes, probably because that geographic region is where both wheat and Bgt originated. These recent Pm genes could be useful sources of resistance in wheat breeding for several regions of the world where powdery mildew is a problem.

Technical Abstract: The globally distributed causal agent of powdery mildew on wheat, Blumeria graminis f. sp. tritici (Bgt), is one of the most rapidly adapting plant pathogens and requires monitoring for shifts in virulence to wheat resistance (Pm) genes. Virulence frequencies were assessed in a total of 346 Bgt isolates from 5 countries that had either lately recorded increasing powdery mildew epidemics (Brazil, South Africa and Australia) or not recently been surveyed (Turkey and Russia). The results were compared to previously published surveys of U.S. and Egyptian Bgt (390 isolates). Many of the Pm genes that have potentially been employed longer (Pm1a – Pm17) were shown to have lost effectiveness, and the complexity of virulence to those genes was higher among Brazilian isolates than those from any other country. Some cases of high virulence frequency could be linked to specific Pm gene deployments, such as the widespread planting of cultivar Wyalkatchem (Pm1a) in Australia. Virulence was also assessed to a set of Pm genes recently introgressed from diploid and tetraploid wheat relatives into a hexaploid winter wheat background and not yet commercially deployed. The isolate collections from Fertile Crescent countries (Egypt and Turkey) stood out for their generally moderate frequencies of virulence to both the older and newer Pm genes, consistent with that region’s status as center of origin for both host and pathogen. It appeared that the recently introgressed Pm genes could be useful sources of resistance in wheat breeding for other surveyed regions.