The nematophagous fungus Pochonia chlamydosporia infects and destroys the eggs of root knot and cyst nematodes.  It is associated with the development of nematode-suppressive soils, and is being developed as a biological control agent.  Genetic fingerprinting using PCR provided a method to discriminate between fungal isolates (Arora et al., 1996) and subsequently indicated that isolates grouped according to the host nematode species and the geographic region from which they were first isolated, and that cyst nematode isolates were more genetically variable than those from root knot nematodes (Morton et al., 2003a).  (Oliver Morton, Tim Mauchline and Brian Kerry)

Effectiveness of different treatments on Tomato roots in nematode-infested soils

The serine protease VCP1, produced by P. chlamydosporia, is implicated in infection of nematode egg masses and cysts and may be a host range virulence determinant.

 

Effect of V. chlamydosporium on Meloidogyne incognita egg surface (Click image for larger version)

We sequenced the gene from three isolates from root-knot nematodes, and three from cyst nematodes.  We also compared the substrate specificity of the enzyme.  Sequence analysis showed differences in the substrate binding region of the gene, depending on the nematode host from which the fungi were isolated, and enzyme assays confirmed that this correlated with differences in substrate recognition (Morton et al., 2003b).

Regulation of VCP1 expression in the rhizosphere was investigated.  Root exudates were collected from tomato plants grown in sterile hydroponic culture, either infected with M. incognita, or uninfected control plants.  Cultures of P. chlamydosporia were exposed to the exudates to detect any differences in VCP1 production due to the presence of the nematode, but none were apparent.

The host specificity of these fungi was also investigated in pot tests where tomatoes were infected with either root-knot or cyst nematodes.  Although all isolates could infect eggs from either nematode to some extent, preference for the original host was apparent (Mauchline et al., 2004).  (Oliver Morton, Tim Mauchline, Brian Kerry and Penny Hirsch)

References:

Arora, D.K., Hirsch, P.R,. & Kerry, B.R. (1996)  PCR-based molecular discrimination of Verticillium chlamydosporium isolates.  Mycological Research 100, 801-809.

Morton, C. O., Mauchline, T. H., Kerry B. R. & P. R. Hirsch (2003a).  PCR-based DNA fingerprinting indicates host related genetic variation in the nematophagous fungus Pochonia chlamydosporia. Mycological Research 107: 198-205.

Morton, C. O., Hirsch, P. R., Peberdy, J. P. & Kerry B. R. (2003b). Cloning of and Genetic Variation in the Protease VCP1 from the nematophagous fungus Pochonia chlamydosporia. Mycological Research 107: 38-46.

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