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|Document Type: ||Thesis or dissertation|
|Title: ||Factors affecting the performance of ochonia Chlamydosporia as a biological control agent for nematodes|
|Authors: ||Esteves, Ivania|
|Supervisors: ||Kerry, Brian|
|Issue Date: ||Jan-2007|
|Abstract: ||The work developed in this thesis aimed to increase understanding about the
variability and stability in eleven biotypes of Pochonia chlamydosporia, a facultative
parasitic fungus with potential as a biological control agent against root-knot
(Meloidogyne spp.), false root-knot (Naccobus spp.) and cyst nematodes (Heterodera
and Globodera, spp.).
Differences in performance were assessed by measuring saprophytic and
parasitic growth using in vitro bioassays. Information on virulence (in vitro) was
collected for a range of biotypes with the objective to relate in vitro parasitic growth
with rhizosphere colonisation ability and secretion of extracellular enzymes. Results
showed differences between biotypes in their ability to colonise the rhizosphere of
plants, parasitise nematode eggs and to produce a range of extracellular enzymes but no
significant relationships were found between saprophytic or parasitic growth and
enzyme production. For the first time, the specific activity of protease, chitinase,
esterase and lipase enzyme production by eleven biotypes of the fungus was examined.
Enzymatic activity was shown to vary with the biotype and type of enzyme assayed and
biotypes could be ranked according to their similarities in enzyme production
A novel bioassay to estimate egg parasitism using liquid media highlighted the
importance of nutrition in infection processes and suggested that all biotypes are able to
infect large numbers of eggs rapidly if the conditions are favourable. The assay reliably
detected fungal infection in nematode eggs within 48 hours and provided a simple, rapid
assay to test the effect of specific nutrients at controlled concentrations on the infection
process. Differences in infection rates between biotypes observed in previous tests on
agar were not detected in the new assay in which nematode eggs and fungal conidia
were added in suspension. Internal colonisation of individual whole Meloidogyne spp.
eggs by P. chlamydosporia was observed using microscopy studies. The destruction of
nematode eggs infected with the fungus within seven days, was confirmed.
The in vitro formation of appressoria was studied in a range of P.
chlamydosporia biotypes. for the first time. Biotypes were found to differ in their ability
to produce appressoria but this ability was not related to differences in virulence (in
vitro) against nematode eggs. Cont/d.|
|Appears in Collections:||PhD, EngD and MSc by research theses (Cranfield Health)|
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