VIEW ARTICLE

Ecology and Epidemiology

Influence of Pine Bark, Matric Potential, and pH on Sporangium Production by Phytophthora cinnamomi. D. M. Benson, Professor, Department of Plant Pathology, North Carolina State University, Raleigh 27695; Phytopathology 74:1359-1363. Accepted for publication July 17, 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-1359.

Sporangium production on mycelial mats of Phytophthora cinnamomi was compared in pine bark and in a Cecil clay soil at controlled matric potentials of 0 to - 150 mb. Optimum sporangium production occurred between - 15 and - 25 mb in both substrates. Sporangium production was markedly less at - 10 mb and at - 150 mb in both pine bark and soil. Matric potential, not water content of the medium, regulated sporangium production. Maximum numbers of sporangia were produced 1 day after mats of mycelium were placed in the tensiometers at a constant matric potential of - 25 mb. Incubation of mats for an additional 1- 3 days did not increase sporangium production. Pine bark at pH 3.7 suppressed sporangium production. At pH 3.5, no sporangia were observed on mats incubated at a constant matric potential of - 25 mb. Air-drying pine bark prior to saturation in Büchner funnel tensiometers completely suppressed sporangium production by P. cinnamomi.