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New research approach required to combat more aggressive and adaptable Phytophthora

July 13, 2001

The potato late blight pathogen has become more aggressive since the arrival of a new type of Phytophthora in Europe circa 1976. Moreover, it is able to genetically adapt to new conditions more rapidly. As a consequence, research aimed at solving the problems caused by this disease must be on a larger scale and involve even greater cooperation than was previously the case.

This is proven by the thesis with which Wilbert Flier recently obtained his doctorate at Wageningen University. Flier's findings support the initiatives taken by the Wagenningen University and Researchcentre to arrive at a ten-year plan for collaboration with government and industry. This plan aims to design compatible tools for a sustained monitoring of the most prominent disease in the cultivation of potatoes, a crop of vital economic significance.

Phytophthora infestans, the pathogen causing late blight, is the major challenge facing potato cultivation both in the Netherlands and in the rest of the world. Vast quantities of pesticides are still required to limit its effects, and the policy of both government and industry is targeted at reducing this practice to a minimum.

A new population of Phytophthora arrived in Europe in or around 1976 from Mexico, which appeared to be a new mating type. Prior to this introduction, the disease could only reproduce by forming spores through vegetative reproduction, with the new generation receiving identical genetic information to their 'parent'.

The extra mating type allows the pathogen (a so-called oomycete) to sexually reproduce. The old form and the new can cross, producing a new generation with a combination of the parents' characteristics and giving Phytophthora a greater genetic diversity.

The spores formed by crossing have a different structure than the ones formed by vegetative reproduction. The cross-bred spores can survive for a longer period of time, up to at least three years according to Flier. This generates greater risks for the parcels of land where potatoes are usually planted.

As a result of the extra means of reproduction, the pathogen has become more flexible in adapting to changing conditions, such as the cultivation of potato varieties with new resistances. There is a greater chance that a new generation of Phytophthora will appear, capable of by-passing the resistance.

Flier has shown how the consequences of the greater flexibility have already become apparent. He has demonstrated that current isolates of Phytophthora are more aggressive those present until 1976. He found indications that the pathogen is increasingly able to overcome the resistance of potato varieties that have displayed a certain level of resistance for many years.

Late blight has also proven capable of infecting potato plants under an even wider variety of conditions. The old form of Phytophthora could only infect successfully in temperatures of between 8° and 23°C, whereas the form that Flier has now found in the fields can operate in temperatures of between 3° and 27° C.

Flier's conclusion is that the Phytophthora problem is an extremely difficult one to tackle, with implications for research and cultivation. In his opinion, there is an urgent need of research that takes a broad and collective approach to this problem, thus enabling the design of basic tools that are both essential and compatible.

In future, potato growers will only overcome the Phytophthora problem if they cultivate in a fully integrated manner. This calls for the breeding of potato varieties with a prolonged resistance to the disease in combination with the use of reliable methods of diagnosis, the alternate use of various pesticides and optimal hygiene in cultivation and agricultural processing.


Wageningen University and Research Centre