First Report of Root Rot of Monterey Pine in California Caused by Phytophthora citricola. C. M. Sandlin, Department of Plant Pathology, University of California, Riverside 92521. M. L. Wadsworth, D. M. Ferrin, and L. Sanchez. Department of Plant Pathology, University of California, Riverside 92521, and Entomological Services Incorporated, Corona, CA 91720. Plant Dis. 76:643. Accepted for publication 10 December 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0643D.
Phytophthora citricola Sawada was isolated from roots of fieldgrown Monterey pines (Pinus radiata D. Don) from Christmas tree plantations in Riverside and San Diego counties in southern California. Diseased trees were severely stunted, the foliage was chlorotic, and roots were sparse and darkly discolored. Trees at both sites had died. To confirm pathogenicity, 15 I-mo-old seedlings in 3-L pots (17.5 X 15.5 cm) were inoculated with an isolate from Riverside County (nine colonized millet seeds per pot); 15 controls were treated in the same manner using noninfested millet seeds. Disease was evaluated 3 mo later. Root rot was evident on all inoculated seedlings, four of which were as stunted and chlorotic as the original diseased trees. The pathogen was reisolated from diseased roots. Mean shoot height, mean dry root weight, and mean dry shoot weight of the inoculated seedlings were 83, 47, and 59% of the controls, respectively. These differences were significant (P < 0.01) as determined by t tests.