from The American Phytopathological Society
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Interpretive Summaries

Soilborne Oospores of Phytophthora infestans in Central Mexico Survive Winter Fallow and Infect Potato Plants in the Field.
S. P. Fernández-Pavía, Instituto de Investigaciones Agropecuarias y Forestales, Universidad Michoacana de San Nicolás de Hidalgo, Morelia, Mexico 58240; N. J. Grünwald, United States Department of Agriculture-Agricultural Research Service, Prosser, WA 99350; M. Díaz-Valasis and M. Cadena-Hinojosa, Campo Experimental Valle de Mexico, CIR-CENTRO INIFAP, Chapingo, Mexico 56230; and W. E. Fry, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Plant Dis. D-2003-1112-01R, 2004 (online). Accepted for publication 14 August 2003.

Oospores are sexual, reproductive structures produced by oomycetes such as the potato late blight pathogen Phytophthora infestans. Oospores can serve as a means of survival of these organisms over a winter because they have thick, double walls that protect the spores. Survival and infectivity of oospores in soils naturally infested with P. infestans oospores were studied in central Mexico. Oospore concentration, viability, and infectivity varied among soils collected during the intercropping period in different locations of central Mexico. In some soils, oospores were infective regardless of the time at which they were collected during the intercropping period. However, oospore viability and infectivity decreased following 2 years of intercropping. This study confirms that oospores can survive over the winter and infect plants in the following growing season in the central highlands of Mexico.