ITS1 region of the rDNA of Pythium megacarpum sp. nov., its taxonomy, and its comparison with related species

Pythium megacarpum sp. nov., was isolated from a soil sample taken from a wheat field in Lille in northern France. It was mistakenly described as Pythium ostracodes Drechsler [Paul, B (1994) Cryptogam.-Mycol. 15,263–271]. Despite morphological resemblance, the comparison between the internal transcribed spacer (ITS)1 regions of the rDNA of the two fungi, leaves no doubt of their different identities. This species is unique because of its large oogonia and plerotic, thick walled oospores, its monoclinous antheridia with large antheridial cells and its lack of zoospores. The character combination of P. megacarpum and the ITS1 sequence of its rDNA, justifies the creation of a new species within the genus Pythium. The fungus is closely related to P. ostracodes. The taxonomic description of this fungus and its comparison with related species, together with the PCR of the ITS1 of its ribosomal nuclear DNA as well as the nucleotide sequences of ITS1 encoding 5.8S rRNA are discussed here.