DECAY CAPACITY OF DIFFERENT STRAINS OF THE BLUE STAIN FUNGUS LASIODIPLODIA-THEOBROMAE ON VARIOUS WOOD SPECIES

Seven strains of the sapwood blue staining fungus Lasiodiplodia theobr omae were studied in the laboratory for their ability to produce cell wall degradation in three broadleaf wood species: Populus tremula, Hev ea brasiliensis and Betula verrucosa and one conifer: Pinus caribaea v ar. hondurensis. Degradation by the strains was determined using weigh t loss in wood substance after 1 to 6 months and by optical and electr on microscopy observations. All L. theobromae strains produce signific ant weight losses and attack in all four wood species after 2 months. Greatest losses often double that recorded for birch, were recorded in rubber wood (ca 18 %) with strain WA1 previously isolated from Khaya ivorensis and in aspen (ca 26 %) with strain IN1 previously isolated f rom rubber wood. These greater weight losses were considered related t o the presence of an easily degradable gelatinous (G-layer) layer in f ibre cells which was rapidly utilized by L. theobromae. The pathway of colonization typically began in vessels and parenchyma cells in the b roadleaf species and resin canals and ray parenchyma cells in the coni fer wood. Ray and terminal or apotracheal parenchyma cells were heavil y colonized; the parenchyma cells were degraded after consumption of t he G-layer in rubber and aspen wood fibres. Decay at a distance by fun gal hyphae of early- and late-wood cells was observed with characteris tic erosion and delamination of the S2 layer and destruction of the S1 -S2 and S1-middle lamellae interfaces. In spite of the apparent morpho logical and physiological variability of the seven strains, L. theobro mae behaved like a typical soft rot fungus producing TYPE 2 erosion ce ll wall decay in the broadleaf wood species. Decay of Caribbean pine c ells was limited primarily to erosion of non-lignified cells reflectin g the known greater importance of lignin type (i.e. guaiacyl) and leve l in hindering cellulolytic fungal attack.