Phytophthora quercina sp nov., causing root rot of European oaks

In a 3 year study of oak decline in Central and Southern Europe, a papillat e homothallic Phytophthora species was isolated consistently, with other Ph ytophthora spp., from necrotic fine roots by direct plating on to selective agar medium and from rhizosphere soil samples by baiting with leaves of Qu ercus robur. The morphology, physiology, RAPD banding patterns and pathogen icity against apple fruits of this Phytophthora sp. are described and compa red with those of other papillate Phytophthora species from Waterhouse's Gr oup I, namely P. cactorum, P. clandestina, P. idaei, P. iranica, P. pseudot sugae and P. tentaculata, and semipapillate Group III P. citricola. The pap illate Phytophthora isolates from oak differed from all other Group I speci es by their uniform, dome-shaped and cottonwool-like colony growth pattern on V8 juice agar and malt extract agar, the frequent occurrence of sympodia lly branched primary hyphae, a high proportion of elongated, ellipsoid or o void oogonia, the absence of amphigynous antheridia and RAPD banding patter ns. Additionally, there was no other species in Group I with as much variat ion in size and shape of the sporangia or large proportion of sporangia wit h a curved apex, hyphal projections, lateral displacement of the papilla an d lateral attachment to the sporangiophore. In pathogenicity tests with inf ested soil, the isolates proved to be more pathogenic to Q. robur than any other Phytophthora sp. recovered from declining oaks in Central Europe. Bas ed on their unique combination of cultural, sporangial and gametangial morp hology, pathogenicity and close association with Quercus but not other tree s, the papillate Phytophthora isolates from oak are described as Phytophtho ra queucina sp. nov.