Susceptibility of Fraser Fir to Phytophthora capsici.

Abstract

Phytophthora cinnamomi, P. drechsleri, P. citricola, and P. cactorum limit Fraser fir production, whereas P. capsici affects Solanaceous, Cucurbitaceous, and Fabaceous crops. Some vegetable growers in Michigan plant conifers for the Christmas tree market in fields infested with P. capsici. To determine the susceptibility of Fraser fir to P. capsici, stems (no wound or 1- or 3-mm-diameter wound) or roots (2 or 4 g of infested millet seed or 2 or 5 × 103 zoospores/ml of a zoospore suspension) of seedlings were inoculated with each of four P. capsici isolates and incubated in growth chambers (20 or 25°C). In addition, Fraser fir seedlings were planted in two commercial fields naturally infested with P. capsici. All P. capsici isolates tested incited disease in the seedlings regardless of incubation temperature or inoculation method. Seedlings (72%) planted in P. capsici-infested fields developed disease symptoms and died. Most of the P. capsici isolates obtained from the Fraser fir seedlings infected while in the field were recovered from root tissue. Identification was confirmed by species-specific direct colony polymerase chain reaction. The pathogen was successfully recovered from stems of all stem-inoculated seedlings, and from roots and stems of all root-inoculated seedlings; the phenotype of the recovered isolate matched the phenotype of the inoculum. This study suggests that planting Fraser fir in fields infested with P. capsici could result in infection and that adjustments in current rotational schemes are needed.