Nature Genet. 48, 201–205 (2016)

Triticale is an artificial hybrid cereal that combines wheat grain quality and yield with the robustness of rye. From its first commercial use half a century ago until 2001, triticale was resistant to powdery mildew, a devastating disease caused by the biotrophic fungus Blumeria graminis. Beat Keller at the University of Zürich, Switzerland, and colleagues now show that the pathogen has adapted to the hybrid cereal by undergoing hybridization itself.

The genomic sequences of different B. graminis strains indicate whether they infect wheat or rye. This also holds true for the newly emerging triticale-infecting isolates, which have large sequences from rye-infecting fungi merged into a mostly wheat-specific genomic background, a hallmark of hybridization followed by backcrossing. So, by combining their genomes, the pathogens have produced a hybrid strain with a host range expanded to include triticale. This event probably took place in Europe sometime after the development of triticale, and has occurred independently at least twice.

The molecular mechanism behind this host expansion is currently unknown, despite the authors checking the ‘usual suspects’ such as secreted effectors. Nevertheless, the discovery that pathogen evolution by hybridization closely mirrors host evolution, even in very short time frames, is of particular interest for agriculture, as it highlights the uncertain future of crop resistance to pathogens.