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Growth of Ectomycorrhizal and Nonmycorrhizal Shortleaf Pine Seedlings in Soil with Phytophthora cinnamomi. Donald H. Marx, Principal Plant Pathologist, USDA Forest Service, Southeastern Forest Experiment Station, Forestry Sciences Laboratory, Athens, Georgia 30601; Phytopathology 63:18-23. Accepted for publication 9 June 1972. DOI: 10.1094/Phyto-63-18.

In a fiberglass-covered, air-filtered growth room, shortleaf pine seedlings (Pinus echinata) with ectomycorrhizae formed by Pisolithus tinctorius or Cenococcum graniforme grew as well in nonsterile soil with Phytophthora cinnamomi (20 propagules/g) as did nonmycorrhizal pine seedlings in nonsterile soil without the pathogen. Nonmycorrhizal seedlings grew well in the absence of the pathogen, but exhibited obvious symptoms (chlorosis, reduced top and root growth) of feeder root disease in soil with P. cinnamomi. Mature ectomycorrhizae were not infected by the pathogen, whereas significant numbers of nonmycorrhizal roots were infected. Ectomycorrhizal development was inversely related to the number of susceptible, nonmycorrhizal feeder roots available for attack by P. cinnamomi.

Additional keywords: biological control of feeder root disease, stabilizing fungal pathogen inoculum.