For healthy potatoes - Bayer CropScience

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The latent period of a pathogen A1-strains, and for the first time, the A2- mating type. These new strains quickly spread throughout Europe. Phytophthora populations deriving from the first wave of migration are referred to as „old“, whereas those from the second migration wave are referred to as “new” populations. Situation in Central Europe Time of infection Appearance of symptoms 3-5 days “new” population, 4-7 days “old” population Fig. 1: The latent period is the time elapsing between infection by the fungus and the first appearance of symptoms. The latent period for the “old” population was between 5 and 7 days. The „new“ population starts to show symptoms within 3 days of an infection event. Many studies have been done to investigate the incidence of Phytophthora populations around the world. The aim has been to determine the relative preponderance and geographical distribution of the “old” and “new” populations. Gene technology methods can be used to characterize populations as being “old” or “new”. Using the polymerase chain reaction (PCR) and gel-electrophoresis, the pathogen’s mitochondrial DNA can be separated out, allowing differentiation between “old” and “new” populations. Investigations at the TU München in 2001 showed that the “old” population comprised less than 4% of the total population in Germany. The situation is similar in neighbouring countries: only a small proportion of the populations in France, Holland, Denmark and Poland is of the “old” type. The population shifts towards a “new” population have also been confirmed in North East Asia and North America. Development of „aggressive“ strains In a number of international studies, it has been possible to distinguish clearly between the “old” and “new” populations. It was found that the “new” population causes a quicker-spreading necrosis, i.e. the pathogen is able to grow more quickly through the leaf. Moreover, the “new” population shows a greater capacity for spore production, with the result that more sporangia are produced per unit area of infected leaf. 14 COURIER 2/06
A further fitness-advantage of the „new“ population is that it has a shorter latent period, i.e. the interval between infection and the appearance of symptoms (see Fig. 1). Whereas the standard latent period quoted for the pathogen Phytophthora infestans used to be 5 to 7 days, isolates collected from the field nowadays show latent periods of less than 3 days. The latent period is a vital indicator in epidemiological terms. A shorter latent period means that more generations can occur within a year. The latent period also has an important influence on the likelihood of success of curative treatments to control of the pathogen. These differences in the properties of the „new“ population indicate that the pathogen is „fitter“: in other words, more aggressive. This increased fitness of the “new” population explains why it has been able to out-compete the old population in most areas of potato cultivation within only a few years. Implications for agricultural practice The results of tests of the effectiveness of curative treatments show that it is almost impossible to prevent the outbreak of an epidemic once infection has become successfully established. Therefore, it is important that the establishment of the pathogen is avoided through preventative measures. A pre-condition for this is the correct timing of the start of the spraying programme, before the first symptoms appear. Computer-aided decision models are an important tool in planning timely fungicide applications. Modern communications media provide the basis for the rapid translation of decision into action. The integration of the latest research results coming from the areas of phytopathology, plant breeding and crop protection will provide the basis for the successful control of the pathogen Phytophthora infestans into the future. ■ New, ultimate protection of potatoes The increasing Phytophthora infection pressure has urged scientific research for the search for new control technologies. With fluopicolide, Bayer CropScience has developed a promising, new-generation active substance for the control of late blight in potatoes. This modern product provides an innovative form of disease control, with a long-lasting action. Fluopicolide is the first active substance in the new class of acylpicolides. It has a novel mode-of-action that allows it to provide effective and sustained control of late blight, targeting all the important stages of the pathogen’s life-cycle. Both direct and indirect germination of the spores and sporangia are inhibited, along with the sexual reproduction of the pathogen. Fluopicolide is an active substance with translaminar properties: following application to the upper side of the leaf, the active substance penetrates the leafsurface and moves into the leaf tissues, providing protection through to the underside of the leaf. If applied to the leaf-base or the petiole, the active substance is distributed towards the leaves: this property means that it is capable of protecting the new growth that develops between successive spray applications. In 2006, Bayer CropScience obtained the first registrations for fluopicolide, in the UK and China. Further registrations are expected in coming years. Fluopicolide is marketed for use in potatoes in a mixture with propamocarb, under the trade name Infinito ® . The two active substances fluopicolide and propamocarb complement each other perfectly: they offer the farmer an effective tool for avoiding the development of resistance. Infinito can also be used against strains of oomycete fungi that are resistant against standard fungicides. Field trials in recent years have demonstrated Infinito’s robust and very high level of action against Phytophthora infestans infections on leaves and stems and tubers. Also the international field trials clearly demonstrated the reliable longlasting protection it brings. Thanks to its very favourable environmental profile, Infinito is suitable for use in integrated crop management programmes and a product of choice for the partners in the food chain. Bayer CropScience is currently testing this highly-active fungicide in trials around the world, in order to develop it into a product for controlling downy mildew in vegetables, ornamental plants and grapes. For example, fluopicolide will be made available for use in grapes in a pre-mix, under the trade name Profiler ® . 2/06 COURIER 15
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For healthy potatoes - Bayer CropScience

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