16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
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The use of copper seed treatments to control potato late blight in organic farming
Keil, S.[1], Benker, M.[2] & Zellner, M.1
Key words: Phytophthora infestans, copper seed treatment, Öko-Simphyt
Abstract
In organic farming potato late blight still is an unsolved problem. Up to now copper fungicides are the only way to control this disease. Delaying the start of the epidemic reduces the need for fungicide usage throughout the growing season. In order to postpone the beginning of the blight epidemic as well as the start of spraying primary stem infections shall be reduced by a copper seed treatment. In field trials these treatments not only reduced primary stem infection but also decreased the number of infected daughter tubers.
Introduction
Potato late blight caused by the oomycete Phytophthora infestans is one of the most important yield-limiting factors in organic farming. The only way to control this pathogen is by the application of copper fungicides. However the use of copper in Germany is limited to 3kg/ha throughout a growing season. An early outbreak of the disease encourages the formation of a fast spreading and massive epidemic, which ultimately can not be controlled with the permitted amount of copper. By reducing the initial infection potential and postponing the beginning of the epidemic sprayings throughout the growing season can be minimized. Thus the primary inoculum must be reduced. The main source for primary inoculum are infected potatoes. These are either tubers missed during the harvest (volunteers), in infected cull piles or potatoes in storage (Andrivon 1997). The latter are nowadays the major problem. Favouring conditions during storage prevent infected tubers from showing symptoms or rotting (Adler, 2001). These latent infected potatoes remain undetected and are used as seed tubers. They are the main source of inoculum as soon as the pathogen starts to produce sporangia, either on the surface of the tuber itself or on the emerged stems. Seed treatments with low volumes of copper shall prevent healthy tubers from being infected and also inhibit latent infected tubers directly from producing sporangia (Benker et al., 2006).
Materials and methods
Seed tubers of the varieties Agria and Quarta were artificially inoculated with zoospores of P. infestans to ensure the appearance of primary stem infections. Subsequently the tubers were treated with copper fungicides (Cuprozin flüssig; 120 grams of copper per ha) and then planted. One approach was performed with tubers from the variety Agria only, inoculated with 50 zoospores. The daughter tubers were analysed for tuber blight by PCR (JudelsonTooley, 2000). In the second approach two tubers were planted closely adjacent to each other, with one of them (variety Quarta) being inoculated with 200 zoospores and the other one (variety Agria) not infected. In this way the effect of the copper seed treatment on the spreading of inoculum from diseased to healthy plants was tested. After emergence visible primary stem infections were measured weekly and confirmed by PCR detection.
Results
The copper seed treatment led to a significant reduction in the number of infected daughter tubers as shown in figure 1.
Figure 1: Effect of copper seed treatment of seed tubers (Cuprozin flüssig; 120 grams of copper per ha) on the infection rate of daughter tubers 2006; different letters indicate significant (p<0.05) differences
Figure 2: Effect of copper seed treatment (Cuprozin flüssig; 120 grams of copper per ha) on primary stem infections of potato plants (variety Agria) planted adjacent to infected Quarta tubers (inoculated with 200 zoospores); different letters indicate significant (p<0.05) differences in the frequency of stem infections; (Puch, 2006)
Infected seed tubers of the variety Quarta caused infections on more than 50% of the neighbouring potato plants (Agria) if neither of the seed tubers were treated with copper. A copper seed treatment of the latent infected tubers slightly reduced the spread of the infection to neighbouring plants. The treatment of the healthy seed tubers with copper fungicides significantly reduced the primary stem infections to 25%.
Discussion
The findings show that copper seed treatments are a promising way of controlling potato late blight epidemics by postponing the outbreak of the primary infections. Since the dosage of the copper used to cover the seed tubers is as low as 48g/t (120g/ha) this way of protecting the plants can be deployed additionally to the normal sprayings without exceeding the maximum allowed amount of copper.
Conclusions
Copper seed treatments decrease primary stem infections significantly and cause a significant reduction of infected daughter tubers
Acknowledgments
This project was funded by the Federal Agency for Agriculture and Food (BLE) within the Federal Ministry of Food, Agriculture and Consumer Protection (BMELV) under the Federal Organic Farming Scheme (BÖL)
References
Adler N. (2001): Untersuchungen zum Befall von Kartoffel mit Phytophthora infestans (Mont.) de Bary mittels visueller Bonituren und PCR-Methoden. Ph.D. Thesis, TU Munich, Germany.
Andrivon D.(1997): Report of the discussion of the subgroup Epidemiology in Lelystad 1996. PAV-Special Report No.1 Applied Research for Arable Farming and Field Production of Vegetables: 12-14
Benker M., Zellner M., Kleinhenz B. (2006): Reduzierung des Phytophthora-Primärbefalls durch eine Kupferbeizung unter den besonderen Bedingungen des Ökologischen Kartoffelanbaus. Mitt. Biol. Bundesanstalt- Land-Forstwirtsch. 400: 329-330
Judelson H.S., and Tooley P.W. (2000): Enhanced Polymerase Chain Reaction Methods for Detecting and Quantifying Phytophthora infestans in Plants. Phytopathology 90(10): 1112-1119
[1]Bavarian State research Centre for Agriculture, Lange Point 10, 85354 Freising, Germany
[2]Chamber of Agriculture North Rhine Westphalia, Siebengebirgstr. 200, 53229 Bonn, Germany