Problem

Production of potatoes is of prime agricultural importance in the Netherlands. Late blight, caused by the oomycete Phytophthora infestans is the most important threat to this crop. Control of the disease is only possible by abundant use of fungicides, which use amounts to more than 50% of all fungicides used in The Netherlands. For more than a century the Phytophthora population was rather uniform and control was possible by integrated crop protection in combination with more or less resistant potato cultivars. However, due to the importation of infected potato material, the Phytophthora population has changed during the last 20 years, becoming more aggressive, producing persistent oospores, and showing more genetic variability, thus enabling adaptation to the present resistant cultivars. The increased aggressiveness, the decrease of resistance and, consequently, the large input of fungicides form a threat to sustainable potato culture in The Netherlands. This threat has led to the Netherlands Initiative on Late Blight (NILB), 2003–2012.

Aim

The aim of NILB is to reduce the use of fungicides to control P. infestans in potato by 75% in 2012 by three strategies. Firstly, to integrate all present and new research in the Netherlands and to focus all projects on this 2012 aim. Secondly, to hand over the steering of all research to a board of representatives from the potato sector to ensure commitment to and application of the results of all short term and long term research. Thirdly, to combine the three parties — research (Wageningen UR), policy (Ministry of Agriculture) and potato sector — in NILB to ensure that each party takes its responsibility for reaching the 2012 aim.

Integrated Research

All research is brought together in six themes that form a highly integrated program (see Fig.1).

Fig. 1.  The results from five themes of short- and long-term research are integrated in the Phytophthora toolbox (theme 6) and translated to be applicable by the potato sector.

Theme 1: Phytophthora Toolbox

Within the Toolbox results from the other five themes will be translated into practical solutions resulting in an integrated control strategy for P. infestans with a minimal input of fungicides. The strategy will have to be adapted to the specific Dutch conditions regarding crop intensity, varieties, pathogen population, pathogen epidemiology, available fungicides, effectiveness of fungicides during the growth cycle, and weather conditions. Integrated practical knowledge will be generated by experimental applied research, on-farm research using different farming systems and by evaluation of farmers' results after applying the new knowledge.

Theme 2: Population Biology

High levels of genetic variation mark P. infestans populations in the Netherlands, which may be associated with the presence of sexual reproduction by means of oospores in diseased crops. This theme is aimed at generating knowledge on functional variation in P. infestans that can be used to improve late blight management strategies and risk assessments.  Research topics are monitoring the various sources of early infections and of specific virulence and genetic diversity, risk assessment of future introduction of new Phytophthora pathogens in Europe from the Andean highlands, evaluation of epidemic fitness components, and studies on mutation rates in P. infestans that lead to fungicide resistance.

Theme 3: Epidemiology

This theme aims to contribute to improved, reliable, year round control strategies through additional (quantitative) insight in the potato late blight disease cycle and epidemic build up. Projects focus on reduction of tuber-born primary inoculum, improved estimates for disease pressure as related to timing and input of chemical control measures, improving yield and yield quality of organic potato by advancing yield formation and increasing the partial resistance level through agronomic measures and physiological optimization of seed tubers. Prototype control measures are evaluated in a practical context in the theme ‘toolbox’.

Theme 4: New sources for resistance

Development of durable disease resistant potato varieties is the most effective way to control late blight. The major resistance genes in the current potato varieties are no longer effective against Phytophthora. In this theme an elaborate and systematic search for new genes is performed in some hundred wild species, related to potato. Whenever new major resistance genes are found, they will be characterized for variation in function and combined by breeding. After testing for resistance, promising material will be handed over to the breeders for integration in their potato breeding programs.

Theme 5: Genomics potato-Phytophthora interaction

The ultimate goal of breeders is to combine resistance genes that confer broad-spectrum resistance to late blight through complementary mechanisms and through the recognition of pathogen factors that are essential for pathogen fitness. However, the fundamental understanding of resistance mechanisms is missing. The aim of this theme is to study the identification of specific genes of potato and Phytophthora, which in the initial stages of an infection detemine the outcome of the interaction. Furthermore, the generation and analysis of defense-related mutants, and the identification and characterization of genes involved in the mon-host resistance to P. infestans in Arabidopsis are studied to unravel the role of key regulators of defense in late blight resistance.T

Theme 6: Genomics of Phytophthora infestans

In this theme current genomic and EST sequence data of P. infestans will be screened as efficiently as possible to identify candidate genes that possibly encode for pathogenicity and (a)virulence factors and to identify variable regions in the genome that can be used for the efficient development of molecular markers. These markers can subsequently be used to study the variation and dynamics of natural P. infestans populations. The final goal is to identify factors that are essential for the overall fitness of the pathogen. The targeting of such factors for chemical control will lead to the development of innovative control strategies.

Organization of NILB

The organization of NILB is outlined in Fig. 2. Central is the Steering Committee with representatives from the stakeholders. Although the Dutch Ministry of Agriculture is financing the major part of the research at Wageningen UR, their role in the Steering Committee is modest. The potato sector (breeders, growers and trade) has the most prominent role in the Steering Committee, as this sector is able to keep research on the applied track and to communicate and implement the results into practice. As shown in Fig. 2 “steering” occurs in two annual loops: one is steering the Wageningen UR research to fill the Phytophthora ‘Toolbox’, another is implementing the toolbox in practice. The implementation is monitored in different farming systems with respect to environmental effects, and problems will be reported to Wageningen UR for feed-back. Whenever a tool is found to be useful and robust, the Steering Committee can make the application of it mandatory for all farmers.

Fig. 2.   Organization-scheme of NILB. The Steering Committee is steering Wageningen UR research as well as communication and implementation of the results.

NILB will stimulate international cooperation with other Phytophthora-research groups in the world.

For further information please contact Piet M. Boonekamp, Plant Research International, Wageningen UR, P.O. Box 16, 6700 AA Wageningen, The Netherlands, Email: piet.boonekamp(at)wur.nl