Location: Foreign Disease-Weed Science ResearchTitle: A re-evaluation of phylogenomic data reveals that current understanding in wheat blast population biology and epidemiology is obfuscated by oversights in population sampling
|FARMAN, MARK - University Of Kentucky
|ASCARI, JOAO - Universidade Federal De Vicosa
|RAHNAMA, MOSTAFA - University Of Kentucky
|DEL PONTE, EMERSON - Universidade Federal De Vicosa
|MARTINEZ, SEBASTIAN - Instituto Nacional De Investigacion Argropecuaria, Urugary
|FERNANDES, JOSE MAURICIO - Brazilian Agricultural Research Corporation (EMBRAPA)
|VALENT, BARBARA - Kansas State University
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/14/2023
Publication Date: 7/24/2023
Citation: Farman, M.L., Ascari, J.P., Rahnama, M., Del Ponte, E.M., Pedley, K.F., Martinez, S., Fernandes, J.C., Valent, B. 2023. A re-evaluation of phylogenomic data reveals that current understanding in wheat blast population biology and epidemiology is obfuscated by oversights in population sampling. Phytopathology. https://doi.org/10.1094/PHYTO-01-23-0025-R.
Interpretive Summary: Wheat blast is a relatively new fungal disease that first emerged in Brazil during the mid 1980s. Although the pathogen that causes the disease quickly spread to neighboring countries, it remained confined to South America until it was discovered during the 2015-16 and 2017-18 cropping seasons in Bangladesh and Zambia, respectively. Wheat blast now poses a serious threat to global wheat production and food security, underscoring the need to understand the population biology and epidemiology to mitigate pandemic outbreaks. Our currently knowledge in these areas is largely based on studies that relied on wheat blast and other isolates collected in Brazil, which led to the conclusion that the wheat blast pathogen is genetically diverse and lacks host specificity. Additionally, these earlier studies also suggested that wheat blast may have originally emerged via a host jump from signalgrass to wheat. Due to inconsistencies in these earlier studies, we reanalyzed the original data from the Brazilian isolates in the context more comprehensive global dataset. Based on this work we conclude that wheat blast is less genetically diverse than previously reported and that the pathogen does indeed show host specificity. Our data also suggests that it is premature to make any inferences into the role signalgrass plays in wheat blast epidemiology. The information in this study provides fundamental information that will be instrumental in combating future global outbreaks of wheat blast.
Technical Abstract: Wheat blast, caused by the Triticum lineage of Pyricularia oryzae (PoT), is a serious disease that first emerged in Brazil and quickly spread to neighboring countries. The recent appearance of this disease in Bangladesh and Zambia highlights a need to understand the population biology and epidemiology of the disease so as to mitigate pandemic outbreaks. Current knowledge in these areas is largely based on analyses of wheat blast isolates collected in Brazil, and their comparison with isolates from non-wheat, endemic grasses. Those studies concluded that wheat blast is caused by a highly diverse P. oryzae population that lacks host specificity and, as a result, undergoes extensive gene flow with populations infecting non-wheat hosts. Additionally, based on genetic similarity between wheat blast and isolates infecting Urochloa species, it was proposed that the disease originally emerged via a host jump from this grass, and the widespread use of Urochloa as a pasture grass likely plays a central role in wheat blast epidemiology. Inconsistencies with earlier phylogenetic studies prompted us to re-analyze the Brazilian data in the context of a comprehensive, global, phylogenomic dataset. We now show that the seminal studies failed to sample the P. oryzae populations normally found on endemic grasses and, instead, repeatedly sampled PoT and P. oryzae Lolium (PoL) members that happened to be present in these hosts. The resulting lack of accurate and representative information about the grass-infecting populations in Brazil means that current conclusions about wheat blast’s evolution, population biology and epidemiology are unsubstantiated and could be equivocal.