Postia

Postia is a genus of fungi belonging to the order Polyporales, widely recognized as significant agents of brown rot in woody plants. These fungi are notorious wood decayers that primarily target the cellulose and hemicellulose components of the cell wall, leaving the lignin intact. This biochemical degradation compromises the structural integrity of both living trees and harvested wood products.

The primary symptom of a Postia infection is the transformation of healthy wood into a dark, brittle, cubical-cracked mass. As the fungus consumes the structural carbohydrates, the wood loses its tensile strength, turns a deep brown hue, and shrinks, resulting in the characteristic cracking pattern known as cubical brown rot. In advanced stages, the wood can be easily crumbled by hand.

These fungi most frequently attack coniferous species, including spruce, pine, and fir, although they are also found on various hardwood species. Entry points usually include mechanical wounds, pruning cuts, frost cracks, or sites of previous insect damage. The fungi can also spread from decaying stumps or infected wood debris residing in the forest floor into the roots and bases of healthy standing trees.

Development and spread are heavily dependent on environmental factors, particularly moisture and temperature. Optimal conditions include high wood moisture content (above 30%) and mild to warm temperatures. During such periods, the fungus produces fruiting bodies that release microscopic spores, which are disseminated by wind or splashing rain to colonize new susceptible wooden surfaces or wounded tissues.

Effective management and prevention of Postia require a multi-faceted approach. In forests, sanitation is key, involving the removal of heavily infected trees and the clearing of decaying debris that harbors inoculum. In timber industries, preventing brown rot involves kiln-drying wood to lower its moisture content below the threshold necessary for fungal growth, combined with the application of wood preservatives for structural materials.