Light microscopic analysis of Tectona grandis L.f. wood inoculated with Irpex lacteus and Phanerochaete chrysosporium

Abstract

Felling of immature teak (Tectona grandis L.f.) trees or delay in transport of wood logs from felling sites provide platform to microbial attack. Among them, white rot fungi are central driving force that degrades wood and causes severe economic loss. In contrast, Phanerochaete chrysosporium and Irpex lacteus are more extensively studied for their ability to degrade synthetic dyes and poly-aromatic compounds. Therefore, in the present study, both the fungi collected from the Gujarat forest were utilised for in vitro decay test to assess their potential in lignin degradation, extent of cell wall damage and pattern of wood decay in sound blocks of teak. In the early stage of fungal inoculation, there was a negligible amount of weight loss; after 1 month it became rapid and highest weight loss (30.05 % by P. chrysosporium and 27.97 % by I. lacteus) was observed at the end of 120 days. Mycelial invasion occurred through vessels, from vessels to axial and ray parenchyma and subsequently into xylem fibres. Both the strains showed selective delignification and the first symptom of degradation was defibration, separation of rays, and formation of boreholes on ray cell walls at an advanced stage. Xylem fibres and parenchyma cells lost their integrity and collapsed completely. Among all the cell types, parenchyma cells and fibres were more vulnerable to fungal attack, while vessels were resistant to the activity of lignolytic enzymes.