White root rot

The fungus Dematophora necatrix (asexual stage of Rosellinia necatrix) is the causal agent of white root rot. This severe soil-borne pathogen attacks the root system, leading to systemic decay and the rapid decline of various woody and herbaceous host plants worldwide.

This pathogen has a wide host range, infecting over 400 species, including economically important crops such as apple, pear, grapevines, peach, and citrus. The disease is particularly destructive in nurseries and orchards where the fungus can spread horizontally through root-to-root contact or infested soil.

Symptoms often appear as foliage chlorosis, premature wilting, and thinning of the canopy. Below ground, the roots are coated with thick, white, fan-like mycelial mats. As the infection progresses, the fungal tissue turns darker, and the roots become brittle and rotten, eventually failing to support the plant’s water and nutrient uptake.

Development is favored by high soil moisture, poor drainage, and warm temperatures. The fungus produces sclerotia and rhizomorphs that allow it to persist in the soil for several years. Even in the absence of a host, it remains viable in decaying organic matter, making eradication from the soil profile an extremely difficult task.

Management strategies focus on preventive measures, including selecting well-drained, disease-free sites and ensuring certified, healthy planting material. Soil solarization or chemical fumigation may be used in specific nursery settings. Once a tree is infected, it should be removed completely, including as much of the root system as possible, to prevent the pathogen from spreading to neighboring healthy plants.