During the course of an investigation on the pythiaceous fungi occurring in burgundian vineyards, three isolates of Pythium were found, all of which were characterised by spherical to lemoniform, proliferating sporangia. Only one out of these three isolates produced sexual characters (S-12) after prolonged incubation, but their asexual structures, temperature growth relationship and molecular characteristics were identical. Saprolegnia-type internal proliferation of the sporangia, and Phytophthora-type lemoniform, papillate sporangia were characteristic of all the three isolates. The type specimen is S-12 which is a medium slow growing saprophyte. The sequence of its ITS region of the rDNA shows a close relationship with the genus Phytophthora. Morphological and molecular characteristics of this isolate justifies its description as a new species: Pythium citrinum. When grown together with Botrytis cinerea, the causal agent of the grey mould disease of the grapevine, this new species shows a pronounced antagonism and suppresses its growth. This new species is very close to P. montanum, a recently described fungus and constitutes a "border species" linking the genera Pythium and Phytophthora. Morphological features of this new species, its antagonism with B. cinerea, the sequences of the ITS region of its nuclear ribosomal DNA, and its comparison with related species are discussed.
Copyright 2004 Federation of European Microbiological Societies