A crucial breakthrough in combating wheat blast, an emerging threat to global food security, has come from an unexpected source.
New research reveals that wheat varieties resistant to another pathogen, powdery mildew, also provide protection against wheat blast.
When seeking resistance to diseases it is common to search among varieties or old landraces from regions where the disease originated. As wheat blast is a disease of humid sub-tropical regions, efforts to control the disease have focused on finding resistance genes among wheat varieties adapted to warmer climates.
According to a press release, a research collaboration led by the John Innes Centre, and including the University of Zürich, challenges this approach, suggesting that researchers should not ignore resistance in wheat varieties that have been bred to withstand other diseases including those of colder climes, like powdery mildew.
Using gene discovery methods developed at the John Innes Centre, researchers have identified the first gene that protects wheat plants against strains of the blast fungus containing the protein effector AVR-Rmg8.
Surprisingly, this gene, located on chromosome 2A of the wheat genome, is Pm4, which confers resistance to powdery mildew, a disease prevalent in the cooler, wetter climates of the northern hemisphere.
The release notes that European plant breeders have been selecting wheat with Pm4 for many years for resistance to powdery mildew; now those in the southern hemisphere will be urged to do the same as protection against wheat blast.
“These findings were completely unexpected, and they suggest that if you want to find resistance to wheat blast you should also look in varieties that come from non-tropical regions, where they already have resistance to mildew,” said Professor Paul Nicholson a group leader at the John Innes Centre and coordinator of the study, which also includes contributions from Mexico-based CIMMYT and Saudi Arabia-based KAUST.
“We need to be open to the idea of looking in unusual places because blast is a disease of high temperature, high humidity environments while mildew is a disease of low temperature high humidity environments so no one would have thought of looking in European varieties previously because one is looking for commonalities.”
The research team discovered this by screening over 300 wheat varieties from the Watkins Collection, a diverse panel gathered worldwide in the 1930s.
Only three percent of this population showed resistance to wheat blast pathogen strains producing AVR-Rmg8. Alarmingly, all highly resistant varieties carried the Pm4 gene, indicating a single resistance source in this diverse population. This highlights the urgent need to identify additional resistances to ensure robust and durable protection against this emerging threat.
The team will now use the same gene discovery methods to search among European-bred wheat varieties for further resistance genes to blast, increasing the genetic armory which can be deployed against this destructive disease.
“This is the first cloned blast resistance gene — unlike previous resistances to blast we have gotten down to the exact gene — even identifying minute variations of the gene that render it nonfunctional,” Dr Tom O’Hara, lead author of the study, said. “This means our findings can be of great immediate benefit for breeders.
“Our aim from the start was to find resistance that was deployable in Bangladesh and potentially other countries where blast has spread to. The added satisfaction is that our study has taken an unexpected twist.”
The wheat powdery mildew resistance gene Pm4 also confers resistance to wheat blast appears in Nature Plants.
