Photo Camille Chauvin

by Camille Chauvin

Research engineer and training manager at ELISOL environnement


co-authors
Cécile Villenave

In agriculture, nematodes are often considered as “enemies” (i.e., like pests responsible for crop damage), yet the most abundant species of soil nematodes have no parasitic activity, therefore they can be your “friends” (by being beneficial to the biological functioning of the soil).

Nematodes are microscopic vermiform organisms (length of about 1mm for a diameter of 20 µm), that are translucent and invisible to the naked eye. They are the most abundant multicellular organisms on earth.

Figure 1: By being microscopic, nematodes represent 1 out of 5 multicellular organisms present on earth! The majority of these organisms are beneficial to the soil’s biological functioning.Photo credit: ELISOL environment

Nematodes are an extremely diversified group (about 20,000 described species) and are present in all environments (fresh water, seas, plants, soils…). Some are parasitic (of vertebrates, invertebrates including insects or plants), others live freely in different environments (soils, rivers, oceans), in all climates and at all latitudes.

Most soil nematodes are beneficial to soil functioning, feeding primarily on bacteria, fungi, and other microscopic organisms including other nematodes.

However, a minority of nematode species attack plants, giving them a bad reputation in agriculture.

Figure 2 : Most soil nematodes are free-living and feed on bacteria, fungi, or other organisms including nematodes (pictured left = bacteriovorous nematodes of the Rhabditidae family). Some feed on plant roots (photo on the right: phytoparasitic nematode of the genus Pratylenchus, a daunting pest ravaging many crops). Photo credit = ELISOL environment

1 - Characterization of nematode populations in the soil is an indicator of soil functioning

Nematodes are located at different levels of the soil micro-trophic chain

What characterizes nematodes is that they are located at different levels of the soil micro-trophic chain and, therefore, their characterization provides information on the whole soil food web

Figure 3 : The soil trophic chain in which nematodes are present at several levels. Each arrow represents a trophic link (who eats whom?)

Valuable bio-indicators

However, if nematodes are particularly interesting for use as bio-indicators of soil condition, it is also because they are present everywhere in high abundance (more than one million per square meter) and present a very high taxonomic and functional diversity. Also, the analytical procedure for the soil nematofauna analysis is standardized (IS0 23611-4).

Finally, a major criterion: they are responsive, in a variable way, to environmental conditions and to physical or chemical disturbances.

 

The various groups of nematodes provide information on soil functionality

Phytophagous nematodes

They provide information on the nature and condition of cover crops and, for susceptible crops, the risk of yield loss.

Figure 4 : Les Meloidogyne sont des parasites extrêmement dangereux, en particulier pour les cultures de tomate. Leurs attaques engendrent la formation de galles caractéristiques et de lourds dégâts sur les productions. Crédit photo : ELISOL environnement, Wikipedia

Microbivorous nematodes

They provide information on the microbial compartment, organic matter dynamics and nutrient recycling.

Figure 5 : By regulating bacteria activity (bacteriovorous nematodes) and fungi (fungus-feeding nematodes: on this picture), microbivorous nematodes optimize the transformation of organic matter and the resulting nutrient flows. Photo credit: ELISOL environment

Omnivorous and predatory nematodes

They reflect physical or chemical disturbances of the environment. They reflect the complexity of food webs, which may underlie the regulatory function of pathogenic organisms.

Figure 6 : Armed with teeth, carnivorous nematodes are able to eat other organisms but also other nematodes. Being indicators of food web structure, they can be active in the regulation of phytoparasite nematodes. Photo credit: ELISOL environment

The study of nematode communities provides various information

  • The level of biological activity of the soil
  • The decomposition of organic matter: predominantly fungal or bacterial
  • The intensity of nutrient flows
  • The complexity of food webs and which may underlie the regulatory function of pathogenic organisms
  • The level of pest pressure related to phytoparasite nematodes

All of these elements are useful for assessing the sustainability of the system.

These innovative analyses regarding soil nematode communities as bio-indicators have been routinely performed since 2011 by the company ELISOL environment, which has also developed specific guidelines (ELIPTO®).
The evaluation of the soil’s bio-function by nematofauna analysis is synthesized in scorecards: for each parameter, the result is located in a reference system specific to the land use (market gardening, field crops, forests, meadows, vineyards or urban soils). The results are scored between 0 and 10, 10 being the best value.

Figure 7 : ELISOL scorecard for the evaluation of the soil’s bio-function by studying the soil nematode community (evaluation of the intensity of the main soil functions supported by living organisms) and information on the parasitic nematodes present within the crop (risk measurement of the pest pressure).

2 - Intense bio-function to regulate the impact of phytoparasite nematodes and other pathogens

Many studies show that soils with complex and diverse food webs tend to limit the development of pathogenic organisms. In fact, the more structured the food webs are and the more important the interactions between organisms are (predation, competition, symbiosis…), which can limit the development of the most opportunistic organisms like phytoparasite nematodes.

Figure 8 : The study of soil organisms in nematode communities provides information on the state of soil food webs and allows us to evaluate the potential for biological regulation of pathogens as well as the impact of agricultural practices on these webs. Photo credit: ELISOL environment

As a bioindicator, nematode communities provide information on the state of soil food webs and make it possible to assess the impact of agricultural practices on soil biological functioning. By studying the entire nematode community, it is possible to select practices that are favorable to soil organisms and unfavorable to pathogens.
This is the case, for example, with crop rotations, crop covers, organic fertilization and reduced tillage. These practices can be implemented as part of an integrated crop protection. However, since the relationships between phytoparasite nematodes and their host plants are specific and the biology of phytoparasite nematodes varies according to the species (reproduction mode, survival time without host, type of parasitism), it is essential to adopt control practices and in particular crop rotations adapted to the problematic nematode species identified on the plot.

So, are nematodes your friends or your foes?

3 - Would you like to know more about it?

ELISOL environment offers a training on soil biology and nematology.

“Nematodes: friends or foes? “is an inter-company training course offering a theoretical and practical approach to better understand these organisms.

 

The presentations cover

– the soil and the biodiversity it shelters.

– the soil nematofauna, a tool for characterizing biological function of the soil.

– the phytoparasite nematodes which are potential crop pests, and how to control them.

 

Whatever the environment: agricultural, natural, or urban, soil is one of the major issues of the 21st century, yet its importance remains underestimated.

Soil nematodes which represent 4/5th of the multi-cellular organisms on earth, are largely unknown.

Whether they be your friends or your enemies, they are a real source of information!

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