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Susceptibility of Sand Pine to Phytophthora cinnamomi. Eldon W. Ross, Principal Plant Pathologist, USDA Forest Service, Southeastern Forest Experiment Station, Forestry Sciences Laboratory, Athens, Georgia 30601, The senior author is now Assistant Chief, Forest Disease Research, Division of Forest Insect and Disease Research, USDA Forest Service, Washington, D.C. 20250; Donald H. Marx, Principal Plant Pathologist, USDA Forest Service, Southeastern Forest Experiment Station, Forestry Sciences Laboratory, Athens, Georgia 30601. Phytopathology 62:1197-1200. Accepted for publication 28 April 1972. DOI: 10.1094/Phyto-62-1197.

Phytophthora cinnamomi is reported as a new, virulent pathogen of sand pine. Ocala and Choctawhatchee races of sand pine seedlings with and without ectomycorrhizae were planted in soils with ca. 27 propagules of P. cinnamomi/g of soil. Ectomycorrhizae were synthesized by Pisolithus tinctorius. Noninoculated mycorrhizal and nonmycorrhizal seedlings of both races showed statistically significant increment in dry weight of foliage and roots and in number of new lateral roots; seedlings inoculated with Phytophthora cinnamomi showed nonsignificant increment in foliar and root dry weight and significant decrease in number of new lateral roots. Mortality of mycorrhizal and nonmycorrhizal seedlings was much higher for the Choctawhatchee race than for similarly treated Ocala race seedlings. High mortality rates were attributed to invasion of nonmycorrhizal roots by P. cinnamomi; ectomycorrhizae were not penetrated by the pathogen. This proof of pathogenicity of P. cinnamomi and its association with areas where sand pine mortality was caused by Clitocybe tabescens suggest its involvement in the etiology of a sand pine-root disease complex.