Large-leaved lime (Tilia platyphyllos) has a low ability to compartmentalize decay fungi via reaction zone formation

The growth of three basidiomycetes (Inonotus hispidus, Fomitopsis pinicola and Ganoderma adspersum) and one ascomycete (Ustulina deusta) was studied within the reaction zone (RZ) of large-leaved lime (Tilia platyphyllos) and host responses were compared with those formerly described in beech (Fagus sylvatica). The main objective of the study was to determine whether antimicrobial differences in host response and fungal growth within reaction zones exist. The cell lumina in the RZ contained only sparse occlusions, which were easily degraded and did not prevent the passage of hyphae between adjacent cells via pits when RZs within excised wood blocks were challenged in vitro with the decay fungi. In a comparison of extracts from the RZ of large-leaved lime and the stronger RZ of beech, differences were found in the concentrations and composition of induced antimicrobial compounds. The RZ of large-leaved lime was relatively weak, compared with the static RZ of beech, and migrated into the functional sapwood at an active microbial invasion front as a result of a dynamic interactive process. These observations support previous interpretations that certain defence mechanisms in the xylem of trees are a means of maintaining hydraulic integrity, rather than physical and chemical barriers, which restrict or inhibit fungal growth.