Foliar Blight and Root Rot of Container-Grown Giant Redwood Caused by Phytophthora citrophthora. C. M. Sandlin, Graduate Research Assistant, Department of Plant Pathology, University of California, Riverside 92521. D. M. Ferrin, Assistant Professor, Department of Plant Pathology, University of California, Riverside 92521. Plant Dis. 77:591-594. Accepted for publication 10 December 1992. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/PD-77-0591.

Phytophthora citrophthora was isolated from the blighted foliage of container-grown giant redwoods (Sequoiadendron giganteum) grown under overhead irrigation at a nursery in southern California. The isolate caused both foliar blight and root rot when inoculated onto greenhouse-grown redwood seedlings. Scanning electron microscopy of the foliar blight stage showed that zoospores aggregate at and infect via stomata. Inoculation of the roots of 1-mo-old seedlings resulted in a significant reduction in the mean dry weight of the foliage after 3 mo (51.1 and 33.6 g for the uninoculated and inoculated treatments, respectively) and a change in the morphology and distribution of the roots within the pots. Isolates of P. citrophthora from Penstemon, Ceanothus, and Citrus and an isolate of P. parasitica from Pinus pinea also caused foliar blight.