Oleksandra Shabliy

Title: Strategies to Improve Resistance to Wheat Powdery Mildew

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About Oleksandra

Oleksandra is a Master’s student in the Department of Plant Pathology. Originally from Kyiv, Ukraine, she earned her B.S. in Biotechnology and Bioengineering from the National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute.” Her undergraduate work focused on industrial biotechnology and the development of microbial production processes for pharmaceutical compounds. Oleksandra previously worked at the Institute of Microbiology and Virology of the National Academy of Sciences of Ukraine, where she was involved in research related to microbial biodegradation and bioenergy production. Her current research focuses on wheat root endophytic Actinobacteria and how they may help wheat tolerate drought stress, suppress soilborne pathogens, and maintain plant health under stressful growing conditions. In her free time, Oleksandra enjoys spending time with her friends, hiking, and doing jigsaw puzzles

Abstract

Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), ranks among the most significant foliar diseases affecting wheat globally. Annual yield losses are estimated between 7.6% and 19.9% in affected regions (1). Research indicates that this pathogen originated in the Fertile Crescent and expanded with wheat cultivation, enhanced by human migration and trade, which influenced its global spread (2).

Powdery mildew is hard to control because Bgt is an obligate biotrophic fungus and has adapted to resistance used in breeding programs. Many resistance genes (R genes) allow the plant to recognize the pathogen and activate defense responses, but they often function only against specific pathogen strains. As a result, this resistance can lose effectiveness as the pathogen population changes over time (2). Surveys in the U.S. showed that several older powdery mildew resistance (Pm) genes have already been broken down, especially in eastern soft wheat production regions. Pm3a, Pm4a, and Pm17 are some of the main examples, showing that resistance based on a single major gene is often not durable (3).

Because of this, researchers are looking for ways to make powdery mildew resistance more effective and longer-lasting. One approach is gene stacking, in which multiple resistance alleles are combined in a single wheat line. It was shown that stacking multiple transgenic Pm3 alleles gave better field resistance than lines carrying only one allele. This stronger resistance seemed to come from both higher total transgene expression and the combination of different allele specificities. Importantly, the stacked lines did not show negative effects on plant development or yield. In some allele combinations, no powdery mildew infection was observed under field conditions (4).

A second approach focuses on susceptibility genes (S genes) instead of R genes. Editing the wheat MLO-B1 locus produced the mutant Tamlo-R32, which had strong powdery mildew resistance without the growth and yield losses often seen in earlier mlo mutants. This line carried a 304-kb deletion in the MLO-B1 region and maintained normal plant height and grain yield while greatly reducing fungal colony formation (5).

A third approach is to introduce resistance genes from wild relatives to broaden the wheat resistance gene pool. Durum wheat was used as a bridge to transfer Pm60 and Pm60b from diploid Triticum urartu into common wheat. Using crossing, backcrossing, and marker-assisted selection, several recombinant introgression types were identified, and resistant lines with high self-fertility were developed. Their results show that wild relatives are still an important source of new resistance genes for improving powdery mildew resistance in wheat (6).

Overall, wheat powdery mildew remains a major challenge because the pathogen continues to overcome widely used resistance genes. However, strategies such as gene stacking, susceptibility-gene editing, and introgression from wild relatives offer promising ways to improve resistance and reduce future losses in wheat (2–6).

Plant Pathology 515, 3^rd Semester, 2^nd Year

1. Sotiropoulos, A. G., Arango-Isaza, E., Ban, T., Barbieri, C., Bourras, S., Cowger, C., Czembor, P. C., Ben-David, R., Dinoor, A., Ellwood, S. R., Graf, J., Hatta, K., Helguera, M., McDonald, B. A., Morgounov, A. I., Müller, M. C., Shamanin, V., Shimizu, K. K., Yoshihira, T., Zbinden, H., Keller, B., and Wicker, T. 2022. Global genomic analyses of wheat powdery mildew reveal association of pathogen spread with historical human migration and trade. Nature Communications 13:4315. https://doi.org/10.1038/s41467-022-31975-0
2. Cowger, C., Mehra, L., Arellano, C., Meyers, E., and Murphy, J. P. 2018. Virulence differences in Blumeria graminis sp. tritici from the central and eastern United States. Phytopathology 108:402-411. https://doi.org/10.1094/PHYTO-06-17-0211-R
3. Singh, J., Chhabra, B., Raza, A., Yang, S. H., and Sandhu, K. S. 2023. Important wheat diseases in the US and their management in the 21st century. Frontiers in Plant Science 13:1010191. https://doi.org/10.3389/fpls.2022.1010191
4. Koller, T., Brunner, S., Herren, G., Hurni, S., and Keller, B. 2018. Pyramiding of transgenic Pm3 alleles in wheat results in improved powdery mildew resistance in the field. Theoretical and Applied Genetics 131:861-871. https://doi.org/10.1007/s00122-017-3043-9
5. Li, S., Lin, D., Zhang, Y., Deng, M., Chen, Y., Lv, B., Li, B., Lei, Y., Wang, Y., Zhao, L., Liang, Y., Liu, J., Chen, K., Liu, Z., Xiao, J., Qiu, J.-L., and Gao, C. 2022. Genome-edited powdery mildew resistance in wheat without growth penalties. Nature 602:455-460. https://doi.org/10.1038/s41586-022-04395-9
6. Zhang, Q., Li, Y., Li, Y., Fahima, T., Shen, Q., and Xie, C. 2022. Introgression of the powdery mildew resistance genes Pm60 and Pm60b from Triticum urartu to common wheat using durum as a ‘bridge’. Pathogens 11:25. https://doi.org/10.3390/pathogens11010025

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