Nematodes are often associated with detrimental effects on crops, yet many nematode families also occupy roles essential to the function of soil systems. Understanding and enhancing beneficial nematode functions can therefore provide a valuable solution to maintaining food security into the future in the face of environmental challenges.
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The burgeoning field of parasitology and its implications
The occurrence of pests and pathogens and the severity of their impacts on agriculture are projected to increase in the future due to changing environmental conditions, increased prevalence of monocultures, and the development of pesticide-resistant strains.
Among pests and pathogens, parasites are considered a major challenge for agricultural production. Parasites encompass many taxonomical groups and are responsible for extensive crop damage, but are also fundamental components of healthy soil systems. Indeed, parasites can also be considered vital bioremediators and agents to control other pests and pathogens.
As such, research efforts have focused on the positive and negative impacts of parasitology in food systems. This is particularly true for nematodes, with the field of nematology gaining momentum in recent years due to the promising implications to protect and enhance food production.
Nematology refers to the study of roundworms and nematodes and has become an independent discipline in the 19th century. The field now overlaps with other subjects in which these taxonomic groups operate and affect, from ecosystem functioning to plant-parasite gene interactions.
Nematodes are the most abundant multicellular organism on Earth. They range between 1 mm and 40 cm and are ubiquitous across nearly all habitats and environments. Moreover, nematodes mostly live a parasitic lifestyle, infecting vertebrates, invertebrates, and plants.
Due to their parasitic nature, nematodes are known to cause extensive economic damage to cultivated plants and can be found in the thousands within only a few grams of soil.
However, the role of nematodes is complex, and they also generate many vital benefits for plants. In a review of plant nematology, author Keith Davies describes the importance of nematodes for plants. The review describes how the most common nematodes in soil systems are bacterial-feeders, fungal-feeders, plant parasites, predators, and omnivores.
Each of these functional groups fulfills various necessary operations to maintain healthy soil systems, and therefore generate several benefits for agricultural food production.
Nematology in agriculture: benefits and practices
According to current studies on nematology, nematodes offer several ecosystem services that affect the nitrogen cycle, decomposition capacity, and control of pests within soil systems.
Firstly, the effects on the nitrogen cycle have generated a growing interest in the beneficial effects of nematodes to improve soil nitrogen content. Specifically, soil disruption, during activities such as tillage, increases nitrogen availability as well as the abundance of bacteria that compete for nitrogen. In response to more bacteria, bacterial feeding nematodes also increase in abundance, and this stabilizes nitrogen availability and increases nitrogen mineralization in soil once again, which is key for crop growth and soil fertility.
Secondly, nematodes are involved in the decomposition of organic matter in the soil. Free-living nematodes are particularly essential as they recycle nutrients in the soil, which is matched by the indirect effect of bacteria and fungi-feeding nematodes that feed on the bacteria and fungi which decompose organic matter. Together, the feeding activity of these nematodes accelerates the decomposition process and makes minerals and nutrients accessible to growing plant roots.
Thirdly, nematodes are valuable biological agents of pest control. Predatory nematodes regulate populations of other organisms in soil as they feed on organisms such as protozoa, insects, and other nematode species. As a result, nematodes moderate the population of other nematodes, and studies have shown that nematodes such as the Steinernematidae and Heterorhabditidae can kill soil-based insect pests within 48 hours.
Finally, nematodes have become key biological indicators of soil health. The diversity and richness of nematodes communities are particularly insightful as they act as proxies to reveal information on the levels of nutrients, fungal availability, and bacteria, in soil. Altogether, nematode communities provide abundant information on soil health and generate a number of benefits for food production systems.
Looking ahead: opportunities for nematology in agriculture
The environmental changes and rising concerns of food insecurity have provided an opportunity to include knowledge from various disciplines into agricultural practices. This is the case for nematology, which offers valuable insights into the dynamics of soil systems and the importance of considering trophic interactions to improve food production.
The implications of considering nematodes to enhance food production can be used to target the increased prevalence of pests and pathogens, improve the resilience of plants to environmental stress, and counteract the reduction in soil quality. Several nematodes may be of particular interest.
For instance, P. hermaphrodita is an example of a slug parasitic nematode, which controls slugs by releasing bacteria inside the host that kills them in about 21 days. P. hermaphrodita is of particular benefit as it is highly effective during wet weather conditions, which is expected to increase in future systems due to the rise of extreme weather conditions such as monsoons and floods. Indeed, given slugs are highly active during these conditions, this species of nematode can be used to eliminate them thus protecting crops.
Other advantages nematodes may provide in future practices to benefit food production include the use of bioengineered nematodes and controlled treatments to eliminate unwanted organisms. This includes certain nematodes themselves such as plant-feeding nematodes, which are detrimental to crops. To improve the resilience of plants to nematode infection, recent studies have improved the identification and breeding of resistant plant genotypes to plant-parasite nematodes.
This would allow plants to survive nematode infections, allowing predatory nematodes to feed upon plant-parasitic nematodes to avoid further crop damage.
A 2017 study by Gregory Bernard et al. reviewed the methods of transcriptome profiling analyses to distinguish nematode-resistant and susceptible plant genotypes and identify the specific molecular components and pathways triggered during the plant immune response to nematode invasion. The review emphasizes the importance of plant-parasitic nematodes in agriculture and the molecular events involved in plant-nematode interactions but highlights the need for more research.
Future nematological studies could focus on quantifying the functional roles of various nematodes and their contribution to functions such as nitrogen cycles and bacteria control. On the other hand, the use of emerging molecular techniques, such as CRISPR-Cas9, would allow plants to develop further resistance to avoid the detrimental effects of plant-parasite nematodes. The balance between detrimental and beneficial nematode species will then further improve crop development into the future, and ensure a more stable level of food security.
- Davies K. G. (2006). Review of Plant Nematology. Journal of nematology, 38(4), 401–403.
- Nickle, W. R. (2020). Manual of Agricultural Nematology (1st ed.). CRC Press.
- Sikora, R. A., Coyne, D. L., Hallmann, J., & Timper, P. (2018). Plant Parasitic Nematodes in Subtropical and Tropical Agriculture (3rd ed.). CABI.
- Singh, S., Singh, B., & Singh, A. (2015). Nematodes: A Threat to Sustainability of Agriculture. Procedia Environmental Sciences, 29, 215–216. doi: 10.1016/j.proenv.2015.07.270