Abstract
Abstract Phytophthora root rot is described for the first time killing sugar pine (Pinus lambertiana) in a seed orchard and four species of true fir (Abies spp.) in a forest nursery. P. cactorum was recovered from true firs and P. megasperma was recovered from sugar pine. P. cryptogea was recovered from sugar pine and true fir but isolates from the two locations differed from each other in pathogenicity and colony appearance. Isolates recovered from these hosts and isolates of 6 Phytophthora species previously recovered from Douglas‐fir (Pseudotsuga menziesii) were then tested for pathogenicity on seedlings of 9 Northwest conifers. P. megasperma Group 1, P. cryptogea, and P. cinnamomi were pathogenic to all tree species except western redcedar (Thujaplicata). Western hemlock (Tsuga heterophylla) and true firs were susceptible to most species tested; ponderosa (P. ponderosa) and sugar pines were damaged only by P. cryptogea and P. cinnamomi; western redcedar was resistant to all isolates.
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