Anatomical characterisation and in vitro laboratory decay test of different woods decayed by Xylaria hypoxylon

Abstract

Different species of Xylaria are often reported as an endophyte in different groups of plants starting from liverworts to angiosperms. In the present study, Xylaria hypoxylon isolated from branch stubs of living trees was utilised for in vitro decay test to investigate the pattern of cell wall alterations in sound wood blocks of Azadirachta indica, Leucaena leucocephala, and Tectona grandis. Naturally infected as well as in vitro decayed wood showed cavities and erosion troughs at the lumen surface. In laboratory decay test, vertical invasion of mycelia occurred through the lateral wall pits of the vessels and vessel-associated parenchyma while ray cells enabled radial movement of mycelia. At the end of 60 days, the progression of degradation in the fibre cell wall was evident by the formation of transverse boreholes in the cell walls, erosion troughs at the lumen surface, and larger cavities in the S2 layer of secondary wall. The erosion channels were angular to round (i.e. V-shaped or U-shaped). Fungus was also tested for polyphenol oxidase (Bavandemm's test) production by on-plate assay and was found to be positive. Confocal microscopy revealed delignification pattern during degradation of cell wall of different cell types in all the three woody species. The SEM analysis of degraded wood showed the ultrastructural changes in the cell wall particularly penetration of hyphae through the S2 layer of the cell walls forming tunnels through it.