Olpidium root rot

Pathogen and disease type. The causative agent of this disease is Olpidium radicale, a soil-borne fungus belonging to the Chytridiomycota phylum. It functions as an obligate parasite that infects the root system of various plants. The disease is primarily categorized as a root rot or root necrosis, often complicated by its role as a vector for various plant viruses, such as cucumber necrosis virus.

Affected crops. This pathogen has a wide host range, posing a significant threat to intensive greenhouse vegetable production. Primary targets include cucumbers, tomatoes, peppers, lettuce, and various Brassica species. It is particularly destructive in hydroponic systems and soil-less cultivation setups where the pathogen can spread rapidly through circulating water.

Symptoms and signs. Initial signs include stunted growth, wilting of the plant canopy, and chlorosis of the lower leaves. A closer examination of the roots reveals browning, necrosis, and general decay. The root system becomes unable to take up water and nutrients efficiently, leading to reduced fruit yield and, in severe cases, the complete collapse of the plant.

Conditions for development and spread. The fungus thrives in high humidity and waterlogged conditions, with optimal infection occurring at temperatures between 15°C and 22°C. The motile zoospores move easily through irrigation water, drainage, and damp soil particles. It is frequently introduced into new areas through infested water sources, contaminated tools, or infested plant debris left in the growing medium.

Harmfulness and control measures. The economic impact is substantial due to loss of yield and increased production costs associated with disease management. Effective control measures include:

• Strict sanitation protocols for greenhouse equipment and growing media.
• Disinfection of irrigation water using UV systems or specialized filtration.
• Implementation of crop rotation and proper removal of infected plant residues.
• Application of certified biological fungicides and maintaining optimal nutrient balance to improve plant resilience.