Phytophthora irrigata, a new species isolated from irrigation reservoirs and rivers in Eastern United States of America.

A new species of Phytophthora, previously referred to as the 'Dre I' taxon, is named Phytophthora irrigata. Isolates of P. irrigata morphologically and physiologically resemble Phytophthora drechsleri. They are heterothallic, produce nonpapillate sporangia, and grow well at 35 degrees C. The above two species differ significantly in uniformity of mycelium, presence of chlamydospores, DNA fingerprint, and sequences of multiple nuclear and mtDNA regions. Phytophthora irrigata produces smaller sporangia and a distinct DNA fingerprint. Sequence alignments in the ribosomal DNA internal transcribed spacer regions place Phytophthora fallax and Phytophthora captisoa as its closest relatives. The optimal temperature for culture growth is above 30 degrees C and the maximum temperature is 40 degrees C. This new species is abundant in irrigation reservoirs and natural waterways in Virginia and was also isolated in Pennsylvania.