A New Phytophthora sp. Causing a Basal Canker on Beech in Italy.

Abstract

In autumn 2001, bleeding cankers were observed on the basal portion of the trunk of a declining tree in a forest stand of European beech (Fagus sylvatica L.) in Latium (central Italy). A Phytophthora sp. was isolated consistently from infected trunk bark using whole apples as bait. Isolations were made from brown lesions that developed in the apple pulp around the inserted bark pieces. Pure cultures were obtained by using hyphal tip transfers. Colonies were stellate on V8 juice agar (V8A), uniform to slightly radiate on cornmeal agar, and cottony, without a distinct growth pattern on potato dextrose agar (PDA). On V8A, radial growth rates were 2.1, 4.8, and 4.5 mm/day at 10, 15, and 20°C, respectively. Colonies grew slowly at 5 and 25°C, but failed to grow at 30°C. On PDA, growth was 1.7 and 1.4 mm/day at 15 and 20°C, respectively. Catenulate hyphal swellings formed on solid and liquid media. Sporangia formed abundantly at 15°C, were ovoid to obpyriform, semipapillate, occasionally bipapillate, and had narrow exit pores (mean diameter = 5.4 μm). On V8A, pores were 40 to 50 μm in length and 25 to 40 μm in breadth. Isolates were homothallic with paragynous antheridia, oogonia were spherical with diameters from 32 to 35 μm, and oospores were plerotic with diameters from 20 to 30 μm. Electrophoretic banding patterns of mycelial proteins and isozymes (alkaline phospatase, esterase, glucose-6-phospate dehydrogenase, malate dehydrogenase, and superoxide dismutase) of beech isolates were distinct from those of reference isolates of semipapillate Phytophthora species, including P. citricola, P. hibernalis, P. ilicis (IMI 158964), P. psychrophila (CBS 803.95), and P. syringae from citrus fruits, whose identification had been confirmed on the basis of internal transcribed spacer (ITS)-restriction fragment length polymorphism (RFLP) patterns and sequences. Conversely, the electrophoretic phenotype and the ITS-RFLP pattern (and sequence) of the beech isolates were identical to those of a reference isolate (Ph24) from Quercus cerris, which was originally identified as P. syringae on the basis of morphological and cultural characters (1). However, the isolate Ph24 has been reexamined, and morphological and cultural characteristics as well as the ITS sequence would indicate that this isolate is a new species not yet formally described, for which the name P. pseudosyringae has been suggested (2). The pathogenicity of a beech isolate (IMI 390500) was compared to that of an Italian P. cambivora isolate from European chestnut by inoculating the stems of 16-month-old beech seedlings (10 replicates), which were placed at 18°C with a 12-h photoperiod. The beech isolate produced lesions averaging 2 cm long after 2 months, while those produced by the P. cambivora isolate averaged 3 cm. Control seedlings inoculated with sterile agar did not develop symptoms. The pathogen was reisolated from lesions to fulfil Koch's postulates. To our knowledge, this is the first report of this new Phytophthora sp. on beech in Italy. Conversely, the same species has been reported to be associated with decline of oak stands (1).