Evolution of the wheat blast fungus through functional losses in a host specificity determinant

Wheat blast first emerged in Brazil in the mid-1980s and has recently caused heavy crop losses in Asia. Here we show how this devastating pathogen evolved in Brazil. Genetic analysis of host species determinants in the blast fungus resulted in the cloning of avirulence genes <i>PWT3</i> and <i>PWT4</i>, whose gene products elicit defense in wheat cultivars containing the corresponding resistance genes <i>Rwt3</i> and <i>Rwt4</i> Studies on avirulence and resistance gene distributions, together with historical data on wheat cultivation in Brazil, suggest that wheat blast emerged due to widespread deployment of <i>rwt3</i> wheat (susceptible to <i>Lolium</i> isolates), followed by the loss of function of <i>PWT3</i> This implies that the <i>rwt3</i> wheat served as a springboard for the host jump to common wheat.