Pressure and Composition of Intrastem Gases Produced in Wetwood of American Elm. C. W. Murdoch, Postdoctoral Research Fellow, New England Plant, Soil and Water Laboratory, USDA, ARS, University of Maine, Orono 04469. C. J. Biermann, Graduate Research Assistant, Mississippi State University, Mississippi State 39762; and R. J. Campana, Professor of Botany and Forest Pathology, University of Maine, Orono 04469. Plant Dis. 67:74-76. Accepted for publication 25 May 1982. Copyright 1983 American Phytopathological Society. DOI: 10.1094/PD-67-74.

Bacterial wetwood of American elm (Ulmus americana) is associated with positive intrastem gas pressures within affected wood. Comparative data were obtained on elemental gas composition and seasonal variation in the magnitude of gas pressure in nondiscolored sapwood and discolored wetwood. Gas composition was determined by gas chromatography, and gas pressures were monitored with a gauge cock. No positive gas pressure was observed in nondiscolored sapwood. Positive gas pressures in discolored wetwood increased from May through August, then declined. Mean gas composition in sapwood and wetwood was, respectively, CO₂, 5.4 and 8.8%; O₂, 18.9 and 7.2%; N₂, 74.7 and 32.8%; and CH₄, 0 and 47.2%. CH₄ levels were significantly higher and O₂ and N₂ levels significantly lower in discolored wetwood, where bacteria abound, than in nondiscolored sapwood, where bacteria are rare.