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Populations of Phytophthora cinnamomi and Pythium spp. Under Shortleaf and Loblolly Pines in Littleleaf Disease Sites. William J. Otrosina, Graduate Research Assistant, School of Forest Resources, University of Georgia, Athens 30602; Donald H. Marx, Principal Plant Pathologist, U.S. Department of Agriculture (USDA), Forest Service, Southeastern Forest Experiment Station, Forestry Sciences Laboratory, Athens, Georgia 30602. Phytopathology 65:1224-1229. Accepted for publication 23 May 1975. DOI: 10.1094/Phyto-65-1224.

Soil populations of Phytophthora cinnamomi and Pythium spp. in stands of Pinus echinata and P. taeda in the Georgia Piedmont district were determined using two selective agar media and an apple trap technique. Littleleaf disease symptoms were moderate-to-severe on P. echinata and absent on P. taeda trees. Soils in most test sites were of the Cecil clay series; one site of each pine species was on Madison clay. P. cinnamomi was isolated from soil under both pine species, but recovery was more consistent under P. echinata. Pythium spp. of the P. irregulare-P. debaryanum complex were isolated more consistently from soil under P. taeda than from under P. echinata. Seasonal differences in soil populations of the different fungi were not detected. Seasonal differences were detected in the capacity of soil extracts to induce sporangium production in P. cinnamomi from under both pine species, but significant differences were not detected between pine species. Extracts from surface soil (0-8 cm) had greater sporangium-inducing capacity than extracts from soil from various depths (10-45 cm) in soil profiles.

Additional keywords: feeder root disease, zoospores, Pythium ultimum.