ADVANCES IN THE UNDERSTANDING OF HEMLOCK BROWNSTAIN

Lumber (hem-fir) cut from western hemlock (Tsuga heterophylla (Raf.) S arg.) and amabilis fir (Abies amabilis (Dougl.) Forbes) trees represen t about 60 % of Canada's west coastal production of wood. Hem-fir is e xported to many overseas destinations where the lumber is highly regar ded for its white or light appearance and fine grain. However, a serie s of complex brown/black discolorations, periodically cause loss in va lue. In this study hemlock brownstain is described microscopically in discoloured hem-fir lumber. Brownstain was most often observed in pare nchyma cells and less often in tracheids. Microorganisms were frequent ly found in discoloured specimens and an association between fungi and bacteria and brownstain was indicated. For the first time catechin an d/or epicatechin were histochemically demonstrated in brown deposits p resent in western hemlock and amabilis fir but also in western hemlock free of brownstain. Three Ophiostoma piceae strains and a mixed bacte rial culture were demonstrated to produce in vitro brownstain in liqui d culture and in western hemlock wood.