Submitted to: Phytopathology Supplement; APSnet (Plant Pathology Online)
Publication Type: Abstract Only
Publication Acceptance Date: 4/30/2008
Publication Date: 6/1/2008
Citation: Weiland, G.E., Nelson, A., Hudler, G. 2008. Aggressiveness of Phytophthora cactorum and Phytophthora citricola isolates on European beech and lilac. Phytopathology Supplement; APSnet (Plant Pathology Online). 98:S168.
Technical Abstract: Inoculation experiments were conducted to compare the aggressiveness of Phytophthora cactorum and P. citricola isolates on European beech and lilac seedlings grown in a greenhouse. The isolates were obtained from bleeding cankers on European beech from five cities (Albany, Ithaca, Oyster Bay, Plainview, and Rochester) in New York. Isolates of P. citricola were subdivided into two clades ( P. citricola 1 and 2) based on distinct differences within selected DNA sequences. Stems, roots, and leaf disks of both hosts were inoculated with three single-spore isolates of P. cactorum , four of P. citricola 1, and three of P. citricola 2. Stems were inoculated with colonized agar plugs, roots via infested soil at three inoculum levels, and leaf disks with a zoospore suspension. Disease incidence was independent of isolate in all inoculated stems and leaf disks (100%) but was dependent on isolate in the soil infestation assay (0-100%) for both hosts. Severity (canker length, rate of mortality, and affected leaf disk area) was dependent on isolate regardless of inoculation site (stem, root, or leaf, respectively) or host, with P. cactorum isolates usually causing less necrosis than either clade of P. citricola . However, the range of disease severity caused by isolates of P. citricola 1 was similar to that of P. citricola 2. Lilac was less severely affected by inoculation than beech, regardless of isolate. No effect of inoculum level on root infection was observed.