[ Slide Set III ] Parasites of Sedentary Stages
There are a large number of fungi that can parasitize nematode eggs, and the sedentary juveniles and females of cyst and root-knot nematodes. These fungi are grouped into two categories: obligate parasites are those that can grow only in nematodes; and facultative parasites are those that can grow to some extent in nematodes as well as on organic matter in the soil.
Obligate Parasites
Nematophthora gynophila and Catenaria auxiliaris
Zoospores of both fungi encyst on the cuticles of young female cyst nematodes, penetrate, and consume the internal contents, including the eggs. Within the nematode body, zoospores develop within sporangia and are released through exit tubes into the soil. Both N. gynophila and C. auxiliaris form resting spores which are more persistant than the fragile zoospores.
Long filamentous exit tubes of N. gynophila protruding from an infected cyst nematode.
Photo by B. R. Kerry
Resting spores of C. auxiliaris that have been released from a crushed cyst nematode.
Photo by E. P. Caswell-Chen
Facultative Parasites
Many fungi found within cysts and within egg masses of cyst and root-knot nematodes are common soil saprophytes and are only weak parasites of nematodes. However, some isolates of these fungi are aggressive nematode parasites.
A fungus designated ARF has colonized a cyst of the soybean cyst nematode. Cysts are dead females, therefore the presence of a fungus in or on the cyst is not a sign of parasitism. If a fungus is an aggressive parasite, most of the eggs inside the cyst will be killed.
Photo by D. G. Kim
An egg of the soybean cyst nematode infected by the fungus ARF.
Photo by D. G. Kim
An egg of the clover cyst nematode containing an unidentified fungus. It is unclear whether the fungus infected a healthy egg or merely colonized a dead egg.
Photo by N. S. Hill
A juvenile of the soybean cyst nematode parasitized by the fungus ARF. The fungus infected the nematode from underneath the mycelial mat formed near the tail.
Photo by P. Timper
Examples of fungi that have been identified as aggressive parasites of sedentary stages of cyst or root-knot nematodes. Not all isolates of these fungi are aggressive parasites. All the fungi are imperfect stages of ascomycetes.
- ARF - an unidentified sterile fungus
- Cylindrocarpon destructans
- Dactylella oviparasitica
- Paecilomyces lilacinus
- Verticillium chlamydosporium
- Verticillium lamellicola
- Verticillium lecanii
- Verticillium leptobactrum
- Verticillium suchlasporium