A weed susceptible to a fungus that can devastate barley crops might be driving the evolution of more aggressive variants of the pathogen, according to new research at the Australian National University.

Celeste Linde, of the School of Botany and Zoology, and colleagues have analysed genetic sequences of the fungus Rhynchosporium secalis, which attacks barley as well as the weed barley grass, common in Australian pasture grasses.

The work, funded by the Grains Research and Development Corporation, was aimed at finding out whether the high level of genetic diversity in the weed was promoting the evolution of more harmful forms of the fungus.

"Barley, like all cultivated crops, is bred for uniformity," says Linde. "The weed is first of all different from cultivated barley and genetically more diverse and may select for a higher level of virulence diversity in the pathogen. Our preliminary results suggest there are more virulent types of the pathogen on barley grass than on barley."

The scientists sequenced genes in 350 samples of the fungus from Australia, comparing the sequences obtained from the barley host with those from barley grass. They were looking for hints on ways to control barley "scald", the disease caused by the fungus.

In cool, humid years favourable to the spread of the fungus up to 40 per cent of barley crops bear the marks of the pathogen, with patches of their leaves blackened as if scalded.

"It reduces the photosynthetic area of the plant, reducing yields and sometimes killing the plant," Linde says.
One method of controlling the fungus might be to eradicate the weed around barley crops to arrest the transfer of spores and destroy the source of genetically diverse pathogenic variants that sustains the fungus between crop growing seasons.

In related research, the scientists used the Rhynchosporium secalis gene sequences to piece together the pathogen's family tree. They found the fungus emerged from a related Rhynchosporium species infecting Agropyron grasses fter barley was introduced to Europe, later spreading around the world with the movement of barley as an agricultural crop.