Nematodes (roundworms) (Kingdom Animalia, Phylum Nemata) are probably the most numerous group of multicellular animals on Earth. They occur in all life areas from marine to fresh water, from the polar regions to the tropics and virtually all habitats.

Among the 20,000 species described so far, a majority are non-parasitic forms free living in the sea, fresh waters and the soil. The forms parasitizing insects, plants or animals (including human beings) are of a great economic importance.

For example, the annual losses attributable to nematodes inflicted upon world crop yields run into billions of dollars and reflect:

-        impaired plant productivity resulting from incapacity of the root system, general weakness and losses incurred in populations in the early phases of development,

-        degraded commercial quality of crop plants (as where carrots display root-knot or ornamental plants are infected by eel-worms or stem-bulb nematodes),

-        distortions and disruptions to the international trade in plant products – especially reproductive material – as a reflection of a high risk of transferring pests, and consequent invasion of various kinds of quarantine.

The harm accruing from the activity of plant-parasitic nematodes entails:

-        mechanical damage of the root cuticle and consequent clearing of the way for soil micropathogens (e.g. fungi and bacteria) to gain entry,

-        suffering plants of nutrients (as these are diverted to the parasites),

-        disturbance of metabolic processes in plants under the influence of exuded digestive enzymes that stimulate division among meristem cells, leading to abnormal growth and development, the dissolution of cell membranes and formation of large giant cells, necrotic changes in the cells surrounding areas damaged by pest feeding, and the transfer in of plant microorganisms; some species may act as vectors of plant viruses, subsequently infecting hosts at feeding sites.

Plants attacked by nematodes have root systems curtailed to the point where possibilities for the uptake of water and nutrients from the soil are impaired, this assuming particular significance in periods or circumstances in which both are anyway in a short supply. The issue of the greatest importance is nevertheless the biochemical change induced in plants.

Difficulties with the identification of nematode species by classical methods (based on a comparison of morphological and anatomical features) are generated by:

-        the microscopic size of most species (plant-parasites are usually less than 1mm long and several tens of microns wide),

-        major individual-level variability to traits within a given population,

-        the relative nature of taxonomic features,

-        the need to obtain an appropriate number of adult specimens (the larval stages of certain species are unidentifiable and regularly account for 60-80% of a population),

-        the degree of complexity and time-consuming nature of the process by which nematode preparations are made.