Olpidium bornovanus

Olpidium bornovanus is a soil-borne fungus belonging to the Chytridiomycetes class, recognized in modern plant pathology primarily as a critical vector for various plant viruses, most notably the Cucumber Necrosis Virus (MNSV). Its biological significance lies in its ability to infect roots, allowing viral particles to enter the plant vascular system through the fungal zoospores.

The host range of Olpidium bornovanus primarily includes members of the Cucurbitaceae family, such as cucumbers, melons, and squash. While it can infect crops directly, its status as a vector makes it a major concern in commercial greenhouse production, especially in hydroponic systems where recirculating water facilitates the rapid spread of zoospores between plants.

Symptoms of the infection are often complex, as they represent a synergy between the fungal damage and the transmitted virus. Infected roots may show minor necrosis or discoloration, but the most diagnostic signs are the systemic viral symptoms on the aerial parts of the plant. These include yellowing (chlorosis), stunting of growth, leaf curling, and distinctive necrotic lesions on the developing fruit, significantly reducing crop yield.

The development of the fungus is heavily dependent on moisture. Olpidium bornovanus produces motile zoospores that require a film of water to move through the substrate or soil to locate host roots. In adverse conditions, it forms resting spores (cysts) that can persist in the environment for several years, making it an extremely resilient pathogen that is difficult to eradicate once it is established in a growing facility.

Management and prevention focus on eliminating the pathogen's access to host roots. Effective strategies include:

• Rigorous disinfection of irrigation systems and hydroponic equipment.
• Using pathogen-free substrates and water sterilization techniques like UV-C treatment.
• Implementation of strict sanitation protocols to prevent soil contamination.
• Usage of resistant rootstocks that limit fungal penetration.