For healthy potatoes - Bayer CropScience

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Phytophthora infestans: a pa Dr. Hans Hausladen, TU München, Center of Life and Food Sciences, Weihenstephan, Germany The first migration phase of Phytophthora infestans occurred about 160 years ago. The late blight pathogen was imported into Europe from central Mexico, spreading to all areas of cultivation within only a few years. The „new“ population was detected in Europe for the first time at the end of the nineteen-seventies. Since then, both mating types A1 and A2 have been prevalent in Europe. This allows sexual recombination, which makes the pathogen able to adapt more quickly. In other words, the “new” population shows increased “fitness”. 10 COURIER 2/06
thogen of global importance Late blight of potatoes, caused by the pathogen Phytophthora infestans, occurs around the world. In many areas, it is considered the most serious disease of potatoes. The pathogen made history in the middle of the 19 th century, when it destroyed almost the entire Irish potato harvest in successive seasons. This brought about a catastrophic famine, in which a million people starved, and which drove more than two million people to leave Ireland for America, including the ancestors of the later US-President, John F. Kennedy. Stem blight The late blight pathogen is still the cause of considerable harvest losses in many regions of the world. Results from field studies show that epidemics typically cause yield losses of between 40% and 70%, depending on varietal susceptibility and environmental conditions. If infection occurs early in the season, the entire harvest can be lost. The financial loss caused by Phytophthora infestans has been estimated at more than US$ 2.7 thousand million in developing countries alone (source: CIP 1 ). As well as reducing yield, the pathogen also causes reductions in quality, which can bring considerable economic penalties. Sources of infection The fungus Phytophthora infestans can spread in two ways: as asexual vegetative mycelium in infected tubers, or as the sexual stage, in the form of resting spores, the so-called oospores. Sexual reproduction requires the presence of two different mating-types. Sexual reproduction is required for oospore formation. These resting spores are probably important for the long-term survival of the pathogen in soil. However, their 1) Centro International de la Papa, Lima (International Potato Center) Leaf blight importance in the infection cycle of the pathogen has not yet been finally determined. Transmission of the pathogen Phytophthora infestans as vegetative mycelium is only possible via infected plant parts. This means that the fungus can only survive in tubers that are not killed off by frost during the winter. Phytophthora can overwinter in tubers via three routes: • potatoes on cull piles • volunteer potatoes • seed potatoes Biological relationships Tubers can become infected while they are still growing, or later, during harvesting operations. If infected tubers are then planted out in the following spring, the pathogen’s mycelium grows intercellularly through the tuber tissues, entering young sprouts as the tuber germinates, and is then carried upwards in a latent form within the shoots. Another route of infection occurs when the fungus sporulates on infected tubers, and the spores thus released succeed in infecting the lower leaves and stem parts. A further route of transmission occurs when spores spread between tubers in soils with high water content. 2/06 COURIER 11
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For healthy potatoes - Bayer CropScience

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