'', shown here. Plant-parasitic nematodes cause significant economic losses to a wide variety of crops. Chemical control is a widely used option for plant-parasitic nematode management. However, chemical nematicides are now being reappraised in respect of
environmental hazard, high costs, limited availability in many developing countries or their diminished effectiveness following repeated applications.
Control of plant-parasitic nematodes Purpureocillium lilacinum was first observed in association with nematode eggs in 1966 Several successful field trials using
P. lilacinum against pest nematodes were conducted in Peru. The Peruvian isolate was then sent to nematologists in 46 countries for testing, as part of the International Meloidogyne project, resulting in many more
field trials on a range of crops in many soil types and climates. Field trials, glasshouse trials and in vitro testing of
P. lilacinum continues and more isolates have been collected from soil, nematodes and occasionally from insects. Isolates vary in their pathogenicity to plant-parasitic nematodes. Some isolates are aggressive parasites while others, though morphologically indistinguishable, are less or non-pathogenic. Sometimes isolates that looked promising
in vitro or in glasshouse trials have failed to provide control in the field.
Enzymes Many
enzymes produced by
P. lilacinum have been studied. A basic
serine protease with biological activity against
Meloidogyne hapla eggs has been identified. One strain of
P. lilacinum has been shown to produce
proteases and a
chitinase, enzymes that could weaken a nematode egg shell so as to enable a narrow infection peg to push through.
Egg infection Before infecting a nematode egg,
P. lilacinum flattens against the egg surface and becomes closely
appressed to it.
P. lilacinum produces simple
appressoria anywhere on the nematode egg shell either after a few
hyphae grow along the egg surface, or after a network of hyphae form on the egg. The presence of appressoria appears to indicate that the egg is, or is about to be, infected. In either case, the appressorium appears the same, as a simple swelling at the end of a
hypha, closely appressed to the eggshell. Adhesion between the appressorium and nematode egg surface must be strong enough to withstand the opposing force produced by the extending tip of a penetration hypha. When the hypha has penetrated the egg, it rapidly destroys the juvenile within, before growing out of the now empty egg shell to produce
conidiophores and to grow towards adjacent eggs. ==Mycotoxins==