The use of an oligonucleotide that hybridizes to DNA sequences interspersed in the genome of members of the genus Phytophthora as an adjunct to morphological criteria in species identification.

An oligonucleotide (primer), designed from a conserved region of the multi-allelic b locus of the basidiomycete fungus Ustilago maydis, generated reproducible PCR fingerprints in Phytophthora species. The primer hybridized in a species-specific manner to nucleotide sequences interspersed in the genome of the closely related members of Phytophthora taxonomic group IV. We recommend the use of this PCR procedure as an alternative method for resolving the close taxonomic affinity of some members of the genus Phytophthora.