The Irish Potato Famine Fungus, Phytophthora infestans (Mont.) de Bary

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The Irish Potato Famine Fungus, Phytophthora infestans (Mont.) de Bary

The importance of the genus Phytophthora, both to humanity and to the development of the science of plant pathology, has been obvious ever since P. infestans devastated the potato crop in Western Europe in 1845. Its greatest impact was the potato blight epidemic in Ireland (Gregory 1983). In 1845 and again in 1848 a third of the potato crop was destroyed by blight, losses at the extremes of previous European experience. Even more disastrously, three-quarters of the crop failed in 1846. In all, one million people died of famine-related diseases (Clarkson 1989) and up to 1.5 million more emigrated (Alexopoulos, Mims, & Blackwell 1996).

After the initial outbreak of
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1996). Family Pythiaceae includes aquatic, amphibious, and terrestrial fungi, most of the last causing serious diseases of economic plants (Alexopoulos et al. 1996). P. infestans is parasitic on members of the Solanaceae (Von Arx 1987), its three major hosts being the potato (Solanum tuberosum L.), tomato (Lycopersicon esculentum Mill.), and the pear melon (Solanum muricatum Ait.) (Abad & Abad 1997). This species is characterized by coenocytic mycelium and the production of biflagellate, motile zoospores (Dowley 1997). The sporangia are formed under humid conditions mainly during the night and are dispersed under dry conditions during the day by wind. They germinate under humid conditions e.g. in a dew droplet. The zoospores enter the host plant through the stomata and cause new infections (Von Arx 1987).

P. infestans is heterothallic and can reproduce sexually in the presence of the opposite mating type. Sexual reproduction follows fertilization of an oogonium by an antheridium resulting in the production of an oospore (Dowley 1997). The complicated life cycle, with very distinct and strikingly different spore forms ranging from motile zoospores to thick-walled oospores, makes control of diseases caused by Phytophthora difficult and challenging (Zentmyer 1983).

The potato blight struck the whole of Europe in the late 1840s.The blight seems to have arrived from the United States in 1844 with a shipment of seed

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