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Previous studies of European populations of the blast fungus ( Magnaporthe oryzae) have shown the existence of five clonal lineages. Three of them were common to different countries, whereas one was specific to Hungary and another was specific to Spain. But these studies were carried out on a limited number of individuals and pointed out a need for more extensive studies in each European rice-growing area. In addition, temporal evolution of M. oryzae populations is also poorly documented. In this study, we focused on Guadalquivir delta region in southern Spain. A total of 186 M. oryzae isolates were collected from various farmer and experimental fields, on diverse cultivars, over the period 1999-2003, and characterized for their genotypic and pathotypic diversity. Five lineages were identified, one of which was detected for the first time in Europe (E6). The E6 lineage, which was collected over the period 2000-2003, became dominant in 2000. Pathotyping confirmed previous results of a narrow diversity for virulence spectrum in European lineages. Five dominant pathotypes were identified, each one corresponding to a single pathotype. Drastic changes in lineage relative frequencies were observed from one year to another. The origin of such changes is discussed. [ABSTRACT FROM AUTHOR]