New diseases of humans, animals and plants emerge regularly. Enhanced virulence on a new host can be facilitated by the acquisition of novel virulence factors. Interspecific gene transfer is known to be a source of such virulence factors in bacterial pathogens (often manifested as pathogenicity islands in the recipient organism1) and it has been speculated that interspecific transfer of virulence factors may occur in fungal pathogens2. Until now, no direct support has been available for this hypothesis. Here we present evidence that a gene encoding a critical virulence factor was transferred from one species of fungal pathogen to another. This gene transfer probably occurred just before 1941, creating a pathogen population with significantly enhanced virulence and leading to the emergence of a new damaging disease of wheat.
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We thank J. Krupinsky and S. Ali for fungal isolates and K. Rybak, J. Hane, D. Holmes and P. Meyer for technical assistance. This work was supported by Organisation for Economic Co-operation and Development (JA00032562), Grains Research and Development Corporation Australia (UMU88, UMU00022 and UMU14), the Swiss National Science Foundation (Grant 3100A0-104145) and the USDA-ARS (CRIS 5442-22000-037-00D and CRIS 5442-22000-030-00D).
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