Wetenschap - 30 augustus 2010

Detection system can smell trouble in potatoes

Attacks from Phytophthora infestans in potatoes can be quickly traced via aroma substances in the air. Wageningen researchers are working on fully automatic 'low-end' detection systems.

When plants are attacked by harmful insects, they raise the alarm by releasing substances such as alcohols and hormonal substances. Plants infected by moulds, viruses and bacteria also discharge similar substances. If these brief spells of signal substances are picked up in time while they are in the air, steps can be taken quickly to combat the diseases. While potato blight caused by P. infestans can now be detected by measuring spores in the air, the spore formation stage is actually too late, says researcher Roel Jansen of Wageningen UR Greenhouse Horticulture. Last year, he used signal substances in the air to show the presence of the pathogen Botrytis cinerea in tomato farming. Now, he and his colleagues declare in the scientific journal Crop Protection that they have detected the aroma substances which potatoes release when infected by P. infestans.
Low concentrations
'When plants are affected, they discharge certain alcohols', Jansen explains. 'Grasses do that when they are mowed, and plants when the leaves are broken by insects or moulds. In addition, the hormonal regulation of plants changes when there is stress. It's a known fact that this can be measured in the air.'
However, the signal substances are present in very low concentrations. Jansen has to first increase the concentration of the substances in the air by passing them through a filter. The concentrated mass is then passed through a gas chromatograph which separates the thousands of substances in the air. If Jansen comes across a few nanogrammes of a particular plant alcohol per litre of air, he knows he is onto something. The gas chromatograph is a glass spiral thirty metres long, but the measuring system can now fit into a suitcase.\
Loss of earnings
The present challenge is to automate the detection process. 'In the lab, the researcher looks at the results to find out where in the column the signal substances are. In practice, this has to be fully automated, so that farmers and horticulturists have to do as little as possible.' In addition, the cost price of the detection system has to be greatly reduced. Today's gas chromatographs are just too expensive.
Jansen hopes that subsequent research will be carried out to modify a sturdy gas chromatograph for detecting plant aroma substances. 'Our aim is to have a detection system applicable for a wider range of crops and available at a cost price of thirty thousand euros. That's a lot of money, but diseases and pests can cost farmers and horticulturists thousands of euros per hectare per year. These include the cost of pesticides, sprays, labour and loss of earnings if the detection of diseases and pests take too long.
Pesticide ban
Jansen is especially optimistic concerning cultivation in greenhouses, where investments and harvests per hectare are much higher than in the open fields. Moreover, he says, the detection system will become even more interesting if the European Union starts to ban many of the pesticides used in the horticultural and the agricultural sectors. That would make it more difficult for farmers to curb diseases and pests by spraying. Such strict regulations would probably only be adopted in five to ten years' time, says Jansen. Meanwhile, this period of time is also needed to develop his advanced system for detecting diseases and pests.

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