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Physiology and Biochemistry

Formation and Properties of Wetwood in White Fir. J. J. Worrall, Research assistant, Department of Plant Pathology, University of California, Berkeley 94720; J. R. Parmeter, Jr., professor, Department of Plant Pathology, University of California, Berkeley 94720. Phytopathology 72:1209-1212. Accepted for publication 15 January 1982. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-1209.

In white fir, wetwood is the usual condition of the heartwood. It is characterized by a moisture content generally equal to or greater than that of sapwood, a slightly lower pH, and a red-brown color. Ray parenchyma is alive and contains starch in the dry-appearing transition zone; at the wetwood border, however, nuclei disintegrate, starch disappears, and phenols accumulate. Osmotic potentials (φ_π) are consistently lower than those in sapwood. Analyses of sapwood and wetwood indicate a selective accumulation of K, Ca, and organic acids in wetwood. The elevated levels of solutes account for much of the observed decrease in φ_π. The data support an osmotic hypothesis to account for accumulation of water in wetwood.