APS Abstracts of Presentations

Susceptibility of Fraser fir to Phytophthora capsici
L. M. QUESADA-OCAMPO (1), D. W. Fulbright (1), M. K. Hausbeck (1)
(1) Michigan State Univ, East Lansing, MI, USA
Phytopathology 97:S95

Phytophthora blight limits production of Fraser fir, an important Christmas tree, causing losses up to 75%. Phytophthora capsici affects primarily vegetable crops worldwide. Crop rotation is limited by the long-term survival of oospores and uninfested fields are difficult to find. Studies to determine new hosts may increase crop rotation efficacy. Fraser fir seedlings were inoculated (no wound or 1- or 3-mm-diameter wound) with P. capsici OP97 and were incubated in growth chambers at 20 or 25°C. Four isolates of P. capsici representative of its diversity were used to inoculate seedlings (no wound or 1-mm-diameter wound) incubated at 25°C. Experiments were conducted twice and controls were included. Seedlings were evaluated by calculating the percentage of branches with bronzing. All P. capsici isolates caused disease in non-wounded and wounded seedlings. Wounded seedlings developed symptoms sooner than non-wounded, but after 5 weeks seedlings incubated at 25°C died. Symptoms developed slower in seedlings incubated at 20°C, they died after 7–8 weeks. The pathogen was reisolated from symptomatic seedlings and the phenotype (mating type and mefenoxam resistance) was confirmed. To our knowledge, this is the first report of P. capsici infecting Fraser fir. This study suggests that planting Fraser fir in fields infested with P. capsici could result in infection.

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