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  • 1 Hungarian Academy of Sciences Department of Plant Pathology, Plant Protection Institute P.O. Box 102 H-1525 Budapest Hungary
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Phytophthora alni is a species hybrid that causes a destructive root and collar rot disease of alders throughout Europe. Its subspecies, P. alni subsp. alni (Paa), P. alni subsp. uniformis (Pau) and P. alni subsp. multiformis (Pam) can be distinguished on the basis of phenotypic and genotypic traits. In this study, we report evidence of an unusual genomic combination of two subspecies occurring in two P. alni isolates from Hungary. These isolates, which had previously been identified as Paa using hybrid-specific PCR primers and morphological traits, exhibited a mitochondrial DNA restriction pattern identical to that of Pau. However, RAPD patterns and isozyme profiles of nuclear genes encoding glucose-phosphate isomerase (Gpi) and malate dehydrogenase (Mdh) of the two atypical isolates were identical to those found in all Paa isolates. Isozyme analysis also revealed a novel allele at the putative Mdh-1 locus in Paa and Pam isolates. The atypical Paa isolates have likely emerged as a result of hybridization events in the P. alni population between Paa and Pau .