TABLE CONTENTS

Ecology of Pochonia chlamydosporia in the Rhizosphere
Kerry, B.R. & P.R. Hirsch
Nematode Interactions Unit, Rothamsted Research, Harpenden, Hertfordshire, AL2 5JQ, UK
Pochonia chlamydosporia is a facultative parasite of a range of nematode pests and has been
widely studied as a biological control agent. It has two developmental phases of growth in
the rhizosphere feeding initially on the exudates from plant roots before contact with cyst and
root knot nematodes induces parasitic development and the colonisation and destruction of
their eggs. The fungus exists as different biotypes based on their host preference, which
affects their population dynamics on the roots and the parasitism of nematode eggs. Using
selective primers and a range of PCR-based methods, competition between fungal biotypes in
the rhizosphere and their selection during the saprotrophic and parasitic phases has been
studied. The nutrition of the fungus has a marked effect on parasitic activity and there is no
simple relationship between the abundance of the fungus in the rhizosphere and its efficacy as
a biological control agent. The factors affecting the transition from saprotroph to parasite are
poorly understood but the regulation of some enzymes involved in the infection process is
known to be affected by nutrient levels in the environment. In in vitro bioassays, there
appears to be a fitness cost for virulence in that virulent biotypes are less rapid colonises of
soil. However, in longer-term trials in pots, slower growing virulent isolates parasitise more
eggs and a number of factors appear to be important in determining the host parasite
relationships of this fungus. Understanding these interactions will help develop more robust
biological control strategies.
5 th International Congress of Nematology, 2008 153