How Do Pathogens Evolve Novel Virulence Activities?

Understanding how pathogens evolve is fundamentally important to protect plant health. However, the more we know, the more we see how many different paths or strategies pathogens can use to overcome our efforts to control them. We are also in a moment of dramatic alterations in the geographic distribution and spread of pathogens due to climate change and global trade that can favor the emergence and reemergence of diseases and the spread of aggressive epidemics. In this review we make an overview throughout the knowns and unknowns about host-pathogen co-evolution, host range expansion, and the external factors that can mediate pathogen evolution, considering the mechanisms by which pathogens generate and recombine the genetic variation that leads to novel virulence activities, including DNA point mutation, transposable element activity, gene duplication and neofunctionalization, and genetic exchange.