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Success stories Published on 26-Feb-2004

Title Blight fight

Since its arrival in Europe in the 19th century, the potato blight fungus has wreaked havoc. Millions died of starvation as potato crops were devastated by this most virulent enemy which simply wiped out the staple diet of whole countries. Although the fungus is still with us, it can now be controlled with copper-based fungicides. But these are now suspected of causing environmental problems. A team of researchers across Europe has been trying to develop alternatives, including agronomic strategies designed to restrict the spread of blight. They are confident they have found a winning solution.

The potato
One of the most devastating plant diseases, potato blight has changed the course of history. The epidemics that destroyed potato crops in Europe in the 1840s caused mass starvation. They led to the Great Irish Famine of 1845 to 1847, when up to 1 million people died and the same number were forced to emigrate.

The disease is caused by a fungus-like organism, Phytophthora infestans, which is dispersed by wind-borne spores that emerge from the stomata of infected leaves in humid conditions. When the spores land on a new leaf surface they enter the leaf stomata and germinate.

The first symptoms of potato blight are small lesions on the leaves, which rapidly spread and cause the leaves to turn brown, wither and die. As the infection advances, the blight attacks the growing tubers, disfiguring them, making them inedible and finally causing them to rot away.

Control of potato blight traditionally relies on copper-based fungicides. Copper is potentially toxic, however, and throughout Europe there are moves to ban it – or at least to reduce permitted levels severely. Indeed, it has already been banned in the Netherlands and Denmark.

Prevention better than cure
But if the use of copper is to be banned, alternative agronomic strategies – ideally preventative rather than curative – must be adopted. What these strategies should be is the extremely complex question which this EU-funded project sought to address. “Our first step was to assess the different farming practices currently in use throughout Europe,” explains its coordinator, Carlo Leifert. “This gave us an insight into the areas on which the various work packages ought to focus.”

The partners first analysed the many blight-resistant varieties grown in different parts of Europe. “However, even this is a very complicated area,” says Professor Leifert. “The resistant varieties that we found in some parts of Europe – in particular, in Hungary – prospered in other climatic conditions, but may simply not be suitable for local markets. The potato that makes the perfect British chip is very different from the one with which the Swiss like to prepare rosti. Tastes, and processing and cooking techniques, vary enormously.”

Spice of life
“On the other hand, the strategy of using different varieties can be successful, especially for the small-scale, organic farmer,” says Leifert. “We have shown, for example, that mixing resistant and non-resistant varieties in the same field can decrease the blight effect in both. We do not fully understand this phenomenon, but a team of statisticians is working to analyse the mechanisms. We have also seen that varieties specifically bred for blight resistance in the 1970s and 1980s proved less than successful – losing their resistance within two or three years. We believe that this was due to concentrating on a single gene which conferred resistance, to which the pathogen quickly adapted. We now tend to consider multiple gene interactions, and hope to breed tolerance which may produce slight, but acceptable disfigurement in the tuber. This appears a better long-term solution.”

Another part of the project considered yield levels on organic farms. “Conventional wisdom says that if you have a blight problem it is because there is a nutritional imbalance,” Leifert says. “We investigated this and found no evidence to support it. But we did find that yields could be increased – sometimes by up to 40% – by substituting composted manure for raw manure or slurry fertilisers. The latter both contain water-soluble nutrients which are quickly washed away. The former is produced by a gradual anaerobic chemical reaction, which takes time and actually supplies the required nutrient to the plant at the time in the growing cycle when it most needs it. It acts as a form of ‘controlled release’ system.”

Under control
The project teams also investigated other aspects. The use of biological control agents proved disappointing. The team tried dozens of different ideas, but none had any significant effect. Advanced irrigation techniques to minimise copper usage while maintaining blight control appear to be more promising. Frequent spraying with ultra-low levels of copper, rather than occasional high-level blasts, proved highly effective. This could have a spin-off effect – too little copper in the soil adversely affects its fertility. Equally, minute traces in crops improve their nutritional value.

The goal now is to ensure that the project results are implemented industrially. “It is important to recognise that we are only dealing with small-scale, organic farmers with a dedicated, local market base,” Leifert cautions. “Mixing varieties in a single field would not be practical for large producers, for example. Burger chains and other very large customers would not accept it.”

Nevertheless, Leifert does expect the partners’ efforts to have a positive impact. 2004 will see farm-scale trials in seven countries, where the best practices developed by the project will be implemented alongside current methods, offering a direct comparison. “We are confident that we will have found new ways to control blight or improve yield – and perhaps both. If these expectations prove to be justified, we will have given organic farmers something they urgently need.”

  • Title
    Development of a systems approach for the management of late blight in EU organic potato production.
  • Reference
  • Programme
    FP5: Quality of Life
  • Contact
    Prof. Carlo Leifert
    University of Newcastle
    United Kingdom
    Fax: +44 166 1831 006
  • Partners
    Federal Research Station for Agroecology and Agriculture, Switzerland
    Research Institute of Organic Agriculture, Switzerland
    Federal Biological Research Centre for Agriculture and Forestry, Germany
    University of Kassel, Germany
    Danish Institute of Agricultural Sciences, Denmark
    Groupe de recherche en agriculture biologique, France
    Institut national de la recherche agronomique, France
    Norwegian Centre for Ecological Agriculture, Norway
    Agricultural Economics Research Institute, Netherlands
    Louis Bolk Instituut, Netherlands
    Plant Research International b.v., Netherlands
    Elm Farm Research Centre, UK