Wheat archive links plant pathogens to sulphur dioxide.
Rising pollution levels have affected the fungi that attack wheat.
By John Lucas
An investigation spanning some 160 years of data has shown how air pollution is linked to plant diseases. The study reveals that industrial emissions directly affect which microbes attack wheat.
Each year, US wheat farmers lose some US$250 million as a result of damage caused by the fungus Mycosphaerella graminicola. And European farmers spend about US$400 million annually on fungicides to control the spread of this pathogen and Phaeosphaeria nodorum, which similarly hits crop yield.
Over the course of the past century, European farmers have seen P. nodorum become more prevalent, and the once dominant M. graminicola fall into the background. This switch baffled plant scientists, who struggled to explain what had happened. Now, a team of researchers believes it understands the reason for this change.
Help from history
An archive of British wheat samples that was started in the autumn of 1843 provided the key to the puzzle. Researchers extracted and sequenced the DNA in this plant matter and measured the pathogens present over the past 160 years.
The team looked specifically at levels of sulphur dioxide, an air pollutant spewed out by industrial installations such as coal-fired power stations. In 1844, for example, the sulphur emitted in Britain registered at about 1 million tonnes a year, and M. graminicola was three times as common as P. nodorum. But as this figure climbed to 6 million tonnes in 1970, the M. graminicola virtually disappeared, and P. nodorum exploded to 100 times its 1844 amount.
"This is the first paper in which you can clearly link, over a long timescale, the population dynamics of two pathogens to changes in environmental pollution," says plant pathologist and team member Bart Fraaije of Rothamsted Research in Harpenden, UK.
The team looked specifically at levels of sulphur dioxide, an air pollutant spewed out by industrial installations such as coal-fired power stations. In 1844, for example, sulphur dioxide emissions in Britain were about 1 million tonnes a year, and M. graminicola was three times as common as P. nodorum. But as this figure climbed to 6 million tonnes in 1970, the M. graminicola virtually disappeared, and P. nodorum exploded to 100 times its 1844 amount.
Fraaije explains that with reduced coal burning over the past two decades (and a subsequent drop in sulphur dioxide emissions), the ratio of these wheat pathogens in Europe has returned to more or less the same as it was in pre-industrial times. The study appears this week in Proceedings of the National Academy of Sciences1.
How exactly might pollution exert this influence on plant disease? Fraaije stresses that the fungi may react differently to increases in rain acidity caused by sulphur dioxide, particularly when it comes to forming reproductive spores. But he adds that the mechanism is likely to be very intricate, involving ozone as well as sulphur dioxide.
Fraaije and his colleagues hope that their study will highlight the influence of human pollution on crops, and will one day lead to better prediction and management of agricultural disease.
News@Nature.com, April, 2005
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