THE INFLUENCE OF SELECTED WOOD ANATOMICAL FEATURES ON THE DEVELOPMENT OF DISCOLORATION AND DECAY IN WOUNDED TREES OF YELLOW-POPLAR

Yellow-poplar wound-associated wood contained a lower proportion of vessels and vessel multiples, smaller vessel diameter and an increased ray density and proportion of ray parenchyma cells as compared to normal wood. Also, fiber and vessel element length decreased in wound-associated wood while the proportion of fibers remained the same as that found in normal wood. All abnormal wood anatomical features in the wound associated wood graded towards those of normal wood with increasing distance from the wound area. Specific gravity of wound-associated wood was always greater than normal wood possibly due to the presence of thick-walled ray parenchyma and scleroid cells. The anatomical response to wounding was the same at each height within each tree. Although growth ring width was not significantly different among all trees studied, wounded-associated wood possessed wider growth rings than wood formed distal to the wound area.;Ray tissue index and the proportion of vessels are relatively simple to determine and use for indirect selection of yellow-poplar trees resistant to the spread of discoloration and decay. Since a large amount of family and tree-to-tree variation exists in the wood anatomical features studied and in the volume of discoloration and decay, it would be possible to incorporate resistance into a tree improvement program.;Increased resistance to the development of discoloration and decay in the wood present at the time of wounding has been associated with fewer vessels and vessel multiples in some yellow-poplar trees. Also, a yellow-poplar tree resistant to the spread of discoloration and decay from a wound contained more ray tissue than a less resistant tree. Ray tissue index is a measure of the amount of ray tissue present and incorporates ray density and the proportion of ray parenchyma. Ray tissue index accounted for a greater amount of the variation in the volume of discoloration and decay than either ray density or ray parenchyma cell content alone. A greater amount of ray tissue could indicate an increased area of ray parenchyma cell to vessel contact, and thus, allow for efficient deposition of fungitoxic compounds into vessels.