Hope from an unexpected source in the global race to stop wheat blast

A major breakthrough in efforts to halt the spread of wheat blast, an emerging threat to international food security, comes from a surprising source.

New research unexpectedly reveals that wheat varieties resistant to another pathogen, powdery mildew, also confer protection against wheat blast. The study is published in the journal Natural plants.

When looking for disease resistance, it is common to look among varieties or old landraces from areas where the disease originated. Because wheat blast is a disease of humid subtropical regions, disease control efforts have focused on finding resistance genes among wheat varieties adapted to warmer climates.

A research collaboration led by the John Innes Center and including the University of Zurich challenges this approach, suggesting that researchers should not ignore the resistance of wheat varieties bred to resist other diseases, including those in climates colder, like powdery mildew.

Using gene discovery methods developed at the John Innes Centre, they identified the first gene that protects wheat plants against strains of the blast fungus that contain the AVR-Rmg8 protein effector.

Surprisingly, the gene – located on chromosome 2A of the wheat genome – is Pm4, a gene that gives wheat resistance to powdery mildew, a disease of the cooler, wetter climates of the northern hemisphere.

European breeders have for many years selected wheat containing Pm4 for its resistance to powdery mildew; now, those in the southern hemisphere will be asked to do the same to protect themselves against wheat blast.

“These results were completely unexpected and suggest that if you want to find resistance to wheat blast, you should also look for varieties from non-tropical regions, where they are already resistant to late blight,” said Professor Paul Nicholson, d ‘a lead group from the John Innes Center and coordinator of the study, which also includes contributions from CIMMYT, based in Mexico, and KAUST, based in Saudi Arabia.

“We need to be open to looking in unusual places, because blast is a disease of high-temperature, high-humidity environments, while downy mildew is a disease of low-temperature, high-humidity environments. Nobody would therefore have thought of it beforehand, we are looking for European varieties because we are looking for commonalities.

The research team made the discovery by examining more than 300 wheat varieties in the Watkins collection, a diversity panel assembled from around the world in the 1930s. Of this population, only 3% showed resistance to pathogenic strains of the wheat blast that produce AVR-Rmg8.

Of concern, all highly blast resistant varieties carried the Pm4 gene, indicating that only one resistance was present among this very diverse population. This highlights the need to identify additional resistances to ensure robust and sustainable resistance against this new threat.

The team will now use the same gene discovery methods to search European wheat varieties for other blast resistance genes, increasing the genetic arsenal that can be deployed against this destructive disease.

Dr Tom O’Hara, lead author of the study, said: “This is the first cloned blast resistance gene. Unlike previous blast resistances, we got to the exact gene, identifying even minute variations in the gene that render it non-functional. This means that our findings can be of great immediate benefit to breeders.

“From the start, our goal was to find deployable resistance in Bangladesh and potentially other countries where the blast spread. The added satisfaction is that our study took an unexpected turn.”