Genome evolution of a pandemic clonal lineage of the wheat blast fungus

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Magnaporthe oryzae pathotype Triticum, the causal agent of wheat blast, is a fungus with devastating implications for the wheat crop. The International Maize and Wheat Improvement Center (CIMMYT) has described wheat blast in a Priority Brief as a "deadly and baffling foe". "Global monitoring of disease appearances, movement, and evolution" and "Genetic and epidemiological research" are two of the four priorities listed by CIMMYT.The disease was originally detected in Brazilian wheat fields in 1985 and quickly spread over most of the South American continent in the following years. In 2016, the first wheat blast pandemic beyond South America hit Bangladesh and affected more than 15 000 hectares of fields, causing huge losses in wheat yield. Less than two years later, Zambian farmers were also struck by the wheat blast pandemic, a first for the African continent. Until recently, there has been no confirmation if this pandemic was caused by the same pathogen which had travelled between the continents or if they were the result of other Magnaporthe oryzae pathogen strains shifting their host species to wheat.To answer this question, our teams at The Sainsbury Laboratory, University College London, and several collaborators throughout the world processed and analysed samples of pandemic wheat blast from the three continents through the OpenWheatBlast open science initiative. Molecular analyses linked the pathogen populations in Zambia and Bangladesh to a single pandemic clone called B71 that originated in South America.Our preliminary analyses revealed that this pandemic clone of the wheat blast fungus is evolving. This project will continue and expand wheat blast genomic surveillance in Africa over the coming years and generate genomics-informed knowledge to guide the response to the pandemic. More specifically, we will rapidly identify the emergence of new variants, determine the precise nature of the underpinning genetic changes, and evaluate the impact of these variants on disease severity. A better understanding of how the pandemic wheat blast fungus evolves should inform knowledge-guided disease management and breeding wheat plants that are better able to resist diseases. Our long-term aim is to fully integrate genomic surveillance in the response to plant health emergencies to improve our capacity to protect plants against crop diseases.