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Last Updated: Tuesday, 12 April, 2005, 17:26 GMT 18:26 UK
Crop archive shows pollution link
Septoria leaf blotch disease in wheat crop (John Lucas)
If left untreated, leaf blotch will substantially reduce yields
Scientists have used the world's oldest, continually running field experiment to show how air pollution affects fungal diseases in wheat.

The Broadbalk experiment, at the UK's Rothamsted Research station, has grown crops on the same land since 1843.

Detailed records and samples over that time have been kept in an archive.

Dr Bart Fraaije and his team used these to show a relationship between two fungal pathogens in plants and the amount of atmospheric sulphur dioxide.

The species, Phaeosphaeria nodorum and Mycosphaerella graminicola, are responsible for leaf blotch, which causes the loss of millions of tonnes of grain worldwide each year.

Farmers in the UK may have to spray a crop more than once a season to keep the latter under control.

Coal powered

The Broadbalk experiment was originally started to investigate the effect of fertilisers on crop yields and the soil.

But its remarkable archive of dried plant material, soil samples and meticulous field records has allowed Dr Fraaije's team to retrieve very different information.

They were able to extract fungal DNA from the archived straw to track changes in the populations of the two pathogens.

Harvest scene in 1880 on the Broadbalk classical experiment (Lawes Agricultural Trust)
Samples over 160 years have been dried and stored in an archive
The occurrence of the two species is reported to have altered over the decades in the UK and elsewhere but the reason for this has remained unclear.

The results of the research, published in the Proceedings of the National Academy of Sciences journal, show the pattern of relative abundance of the pathogens is strongly linked to changes in the atmospheric emissions of sulphur dioxide (SO2).

As SO2 emissions rose during and after the industrial revolution, P. nodorum became prevalent, whilst M. graminicola was scarce.

However, coal burning has declined dramatically over the past 20 years, leading to a decline in SO2 emissions, and the situation is now reversed, with M. graminicola more common.

Climate impacts

Pollutants are known to affect both plants and the diseases that attack them, but the precise way they do this is not always clear - even now with P. nodorum and M. graminicola.

It could be that higher concentrations of the gas directly affect the fungi; but it is more likely SO2 is damaging the plants' tissues in some way which allows the pathogens to thrive.

Broadbalk experiment with Rothamsted farm in the background (Lawes Agricultural Trust)
The Broadbalk experiment continues to this day
"There is a lot of research in the literature to show that plants can respond to pathogens; and sulphur dioxide might have an effect on that - its defence reactions," Dr Fraaije explained.

"Cultivars nowadays can cope much better with stress from the environment. Because of resistant breeding for higher yields, these crops can now also probably better stand the air pollution than in the past," he told the BBC News website.

Dr Fraaije said similar research on a wider range of organisms would help assess the impact of environmental change on biodiversity or to predict disease outbreaks, particularly in relation to climate change.

The work at Rothamsted Research, in Harpenden, was done in cooperation with the University of Reading.

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