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Parasites of Vermiform Stages [ Slide Set II ]
[ Trapping Fungi ] [Adhesive-Spored Fungi ] [ Zoosporic Fungi ]
Fungi that form zoospores
Zoospores are motile spores that are propelled by one or two flagella. When zoospores locate a host, they attach to the nematode cuticle, often near a body opening (mouth, anus, vulva), shed their flagellum, and become sedentary (i.e., encyst). The encysted zoospores infect the nematode cuticle by forming a penetration tube that enters through an orafice or directly penetrates the nematode cuticle.
Zoospores of Catenaria anguillulae (Oomycetes) encysted on Xiphinema americanum. Signs of infection are apparent beneath the cuticle.
Photo by B. A. Jaffee
Sporangium and discharge tube (through which zoospores swim into the soil solution) in tail of Xiphinema americanum.
Photo by B. A. Jaffee
When the resources within the infected nematode are exhausted, the hyphae differentiate to form sporangia. Zoospores are produced within the sporangia and enter the soil via an exit or discharge tube which is formed when the spores are mature.
Zoospore-forming fungi are believed to be opportunistic parasites of vermiform nematodes, attacking or colonizing weakened or dead nematodes. A further limitation of zoospore-forming fungi as biological control agents of nematodes is their requirement for wet soils. Zoospore movement is favored in large, water-filled soil pores.