Rhizina root rot

Rhizina undulata is a destructive soil-borne fungus belonging to the kingdom Fungi, phylum Ascomycota, and order Pezizales. As a specialized pathogen, it is responsible for severe root rot disease, primarily affecting young conifer trees and seedlings in forest ecosystems and nurseries.

The fungus targets various conifer species, including Scots pine, Norway spruce, fir, and larch. Infection typically results in rapid wilting and mortality of young trees, often creating noticeable circular infection centers that expand outward, causing significant losses in reforestation areas and commercial plantations.

The biological cycle of Rhizina undulata is highly dependent on temperature. The mycelium thrives and spreads rapidly when soil temperatures range between 20°C and 25°C. A critical aspect of its ecology is the effect of heat on spore germination; spores are strongly stimulated to germinate by the high temperatures associated with wildfires or campfire sites in the forest.

The pathogen spreads through the soil by contacting healthy roots with infested areas or via mycelial strands. Once it invades the root system, the fungus destroys root tissues, disrupting the tree's vascular transport of water and nutrients. Infected trees show symptoms such as premature yellowing of needles and rapid wilting, often leading to death within a single growing season.

Controlling this pathogen relies heavily on preventive management, as chemical treatments are rarely feasible in forest conditions. Recommended strategies include:

• strictly prohibiting campfires within coniferous stands to prevent heat-induced germination;
• removing stumps and root debris before replanting;
• monitoring infection sites to contain the spread;
• maintaining soil hygiene in tree nurseries;
• ensuring rigorous sanitation during forest management operations to avoid root damage.