Plant-parasitic nematodes: how do we manage them?

PLANT-PARASITIC NEMATODES: HOW DO WE MANAGE THEM?
Nicole Viaene
Institute for Agricultural and Fisheries Research, Merelbeke; Faculty of Sciences, UG, Ghent University,
[email protected]

Plant-parasitic nematodes are a small fraction of the phylum Nematoda, but they have a huge impact
on man by reducing yields of agricultural crops. These microscopic round worms damage plants by
feeding on the plant cell content, by migrating through tissues, and providing entrance for
pathogenic fungi and bacteria into the already weakened plant.
As most symptoms of infection by plant-parasitic nematodes e.g. reduced plant vigour, are not
specific, these organisms are often not recognized as causal agents of crop loss. A first step in
managing plant-parasitic nematodes is adequate detection. This requires appropriate sampling,
extraction and identification techniques. The latter are changing rapidly from morphology-based
identification by specialists using microscopes, to molecular (DNA)-based methods which do not
require such specific training. By making detection methods more accessible and cheaper, diagnostic
laboratories are able to analyze more samples. Plant-parasitic nematodes, the “hidden enemy”, will
become more visible this way, so that the real management can start.

When plant-parasitic nematodes in seeds, wood, flower bulbs or roots are killed by destroying the
(imported) commodity, or by heat-treatment or fumigation; the term control sensu stricto is used.
However, when dealing with nematodes in farmer fields, even the most toxic nematicide is not able
to kill all plant-parasitic nematodes. Moreover, as most nematicides have been banned (at least in
Europe) in the last two decades, an integrated management approach is the only option. This means
keeping population levels of plant-parasitic nematodes below an appropriate damage threshold so
that crop production is possible without economic loss.
Several “old” cultural practices have gained interest again, such as crop rotation, but now using
resistant cultivars or green manures. New variations on old themes are solarisation, inundation and
anaerobic soil disinfestation, but also adding organic matter to soil. Organic amendments give rise to
a larger diversity of soil micro- organisms, including antagonists, and make the soil suppressive
and/or or the plant less vulnerable. Currently, many studies are trying to unravel the complexity of
these mechanisms so that we can understand the processes between soil, plant and nematode. With
the answers we hope to steer the process in the right direction: reducing densities of plant-parasitic
nematodes in the field. This could be done by manipulating the soil environment (e.g. adding
compost, biocontrol organisms, …) or manipulating the plant (e.g. changing genes). The step from lab
and greenhouse trial towards the field environment is the most difficult one, but still needs to be
taken for many of the mechanisms discovered so far.
Last, but really first, is of avoidance or prevention: keeping plant-parasitic nematodes out of the field,
out of a country or a region. International as well as national regulations, including quarantine status,
are very important tools here and even though only a small fraction of harmful nematodes are
detected this way, having rules in place reduces spread. Ways of spread, together with survival and
basic nematode biology have been neglected topics in this era of molecular research. They are,
however, the corner stones of an integrated nematode management.