Air pollution linked to wheat diseases.

Wheat is vulnerable to fungal maladies, known as septoria-blotch diseases, that reduce the ability of the plants' leaves to carry out photosynthesis. For reasons unknown, the relative roles played by the two fungi that cause these diseases--Phaeosphaeria nodorum and Mycosphaerella graminicola--vary from country to country and from decade to decade.

To examine possible factors behind these variations, plant pathologist Bart A. Fraaije of Rothamsted Research in Harpenden, England, and his colleagues tested a library of wheat samples grown on a British farm and archived for most years since 1843. For each year, the team identified which pathogens DNA was more plentiful.

They then compared those data with estimates of emissions of several air pollutants and with meteorological and agricultural records.

After the researchers took into account influences such as growing and harvesting methods and the amount and timing of rain and sun, the effect of sulfur dioxide stood out. The researchers found that as the combustion by-product became more abundant during Britain's industrial revolution, P. nodorum grew more successfully. M. graminicola was relatively more abundant prior to the 1870s and since the 1970s, the latter pattern reflecting recent reductions in sulfur dioxide emissions due to environmental regulations. The team reports its findings in the April 12 Proceedings of the National Academy of Sciences.

The finding doesn't have immediate implications for fighting the agricultural pathogens, Fraaije says. "But it's important to see why these diseases are changing over time," he adds.