Molecular evidence supports Phytophthora quercina as a distinct species

Phytophthora quercina, a new species associated with oak decline in Europe, has been assigned to Waterhouse's Group I of Phytophthora. The level of in traspecific variation and evidence of affinities to other Group I species a nd another, as yet unidentified, species from oak, were examined at the mol ecular level using four random ten-mer primers to amplify total DNA (RAPDs) . Sequences and restriction fragment length polymorphisms of a 900 bp PCR p roduct consisting of the ITS1 and ITS2 regions, and the 5.8S subunit of rib osomal DNA were also examined to estimate relatedness to a broader range of Phytophthora species. The RAPD banding patterns of ten isolates of P. quer cina from eight sites in Germany, Hungary and Italy were almost identical a nd distinct from all the other species tested. Their ITS restriction fragme nt patterns were also identical, as were the ITS sequences of four selected isolates. Phylogenetic analysis of the ITS sequence data confirmed its uni que position in this section of the genus which comprises P. quercina, anot her five Group I species, P infestans (Group IV) and P nicotianae (Group II ). Isolates of P quercina formed a distinct branch at the base of this clad e showing no close affinities with any other species. Such data support mor phological, physiological and pathological evidence that P. quercina is dis tinct, although it has some affinity with the other Group I species. The re sults support earlier reports that Waterhouse's groupings of morphospecies do not fully correspond to phylogenetic relationships indicated by molecula r studies. The unidentified Phytophthora sp. 2 from oak was closely related to P ilicis (Group IV); both were distinct on molecular criteria from all other species in the study.