02388nas a2200229 4500008004100000022001400041245007900055210006900134300001600203490000800219520165000227100001901877700002001896700002401916700001801940700002401958700001701982700001901999700001802018700002202036856010002058 2001 eng d a0953-756200aPhytophthora ramorum sp. nov., a new pathogen on Rhododendron and Viburnum0 aPhytophthora ramorum sp nov a new pathogen on Rhododendron and V a1155 - 11650 v1053 a

Since 1993, a hitherto unidentified Phytophthora species has been found associated with twig blight disease in Rhododendron and, sporadically, Viburnum. The morphology and growth characteristics of fourteen isolates from Germany and the Netherlands were investigated, together with their breeding system, the internal transcribed spacer (ITS) regions of the ribosomal DNA, amplified fragment length polymorphism (AFLP) fingerprints, and isozyme profiles, which were compared to those of a number of outgroup species. Morphologically the isolates are characterized by abundant production of chlamydospores and elongate, ellipsoid, deciduous sporangia with a short pedicel, in which they resemble P. palmivora. However, sporangia were semi-papillate, chlamydospores were much larger and cardinal temperatures much lower than those of P. palmivora. Oogonia with amphigynous antheridia and plerotic oospores were produced in dual cultures with an A2 mating type strain of P. cryptogea. ITS1 and ITS2 sequences of the unidentified species were closest to those of P. lateralis, but differed in three and eight nucleotides respectively from the latter species. AFLP fingerprints and isozyme patterns of malate dehydrogenase (MDH-2) and malic enzyme (MDHP) showed that the isolates formed a homogeneous group, distinct from all examined outgroup species, including P. lateralis. It was concluded that they represent a new Phytophthora species, described here as P. ramorum sp. nov. In pathogenicity tests all isolates of P. ramorum were pathogenic to Rhododendron.

1 aWerres, Sabine1 aMarwitz, Rainer1 aMan_In’t_veld, WA1 aDe Cock, AWAM1 aBonants, Peter, J M1 aDe Weerdt, M1 aThemann, Karin1 aIlieva, Elena1 aBaayen, Robert, P uhttp://www.sciencedirect.com/science/article/B7XMR-4RS3YCS-4/2/9f9142119aa3952d3dbc8811be4860bb