Testing Port-Orford-Cedar for Resistance to Phytophthora

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Abstract
Root rot mortality of Port-Orford-cedar (Chamaecyparis lawsoniana) in western Oregon and Washington and northwestern California is caused almost exclusively by Phytophthora lateralis. Port-Orford-cedar is also susceptible to P. cinnamomi in artificial inoculation but not to other Phytophthora species pathogenic on conifers in the Northwest. Progression of P. lateralis lesions was slower on four cedar trees selected for phenotypic resistance than on randomly selected trees. Inoculations of seedlings and rooted cuttings with zoospores on infested soil and of excised branches with inserted mycelium gave similar results on the selected trees. Branch testing of mature trees and zoospore spray inoculation of seedlings have advantages over other techniques.