Nematodes in soil:
- Nematodes are ubiquitous, found in almost all habitats. Mostly nematodes are parasitic in nature infecting humans, animals, insects and other invertebrates.
- Some other nematodes are plant parasites which can cause economic damage to cultivated plants.
- Nematodes are abundantly present in marine, freshwater, and in soil.
- Soil is an excellent primary habitat for nematodes. Due to microscopic nature of most nematodes, 100 grams of soil contains several thousands of nematodes.
- In soil most of the nematodes exhibit role with agriculture significance and those nematodes are plant parasite nematodes as well as free soil nematodes.
- Free soil nematodes plays significant role in decomposition of organic matters in soil and are beneficial to plants.
- Soil also contains human, animals and insects parasites as in juvenile larval form and mostly parasitic eggs.
- Most of the soil nematodes are present in plant root region in rhizosphere. The soil surrounding the plant root where root exudate migrate and microbiological activity is exceptionally high is called rhizosphere and the surface of root is called rhizoplane.
- Examples: Globodera pallida, Caenorhabditis elegans
Types of nematodes found in soil:
Most nematodes studied on the soil parasitic and they are classified on the basis of their feeding habits. The most common groups of nematodes present in agricultural soil are the bacterial-feeders, fungal-feeders, plant parasites, predators, and omnivores.
- Predatory nematodes feed on protozoa and other soil nematodes whereas Omnivores feed on different foods depending on environmental conditions and food availability
- Omnivorous nematodes primarily feeds on protozoans and other small nematodes as predators. But in the absence of their primary food source, they can feed on fungi or bacteria.
Important role of nematodes in Agriculture and health:
- Nematodes as biological Pest control:
- Some predator nematodes attack and kill a range of pests such as borers, grubs, thrips and beetles with negligible effects on other organisms.
- These nematodes are known as ‘entomopathogenic’ nematodes.
- Nematodes generally feed on smaller organisms like protozoa, bacteria, fungi and other nematodes.
- Some nematodes live in association with specific bacteria that can infects wide ranges of insect pests. When such nematodes infects insects, it releases bacteria that multiplies in host insect and kill them
2. Improve soil fertility; Nitrogen cycle
- Nematodes directly helps in nutrient mineralization through their feeding interactions.
- For example, bacterial-feeding nematodes consume Nitrogen in the form of proteins and other N-containing compounds in bacterial tissues and release excess Nitrogen in the form of ammonium (NH4+), which is readily available for plant use.
3. Decomposition of organic matters:
- Free-living nematodes in soil are very important and beneficial in the decomposition of organic material and the recycling of nutrients in soil.
- Bacteria and fungi feeding Nematode do not feed directly on soil organic matter, but feed on the bacteria and fungi which decompose organic matter.
- The presence of theses nematodes and their feeding activity accelerate the decomposition process.
- Nematodes feeding recycles minerals and other nutrients from bacteria, fungi, and other substrates and returns them to the soil where they are accessible to plant roots.
4. Plant parasitic nematodes:
- Some plant parasitic nematodes infects roots of plants and damage crops. Eg. Globodera
- The mouthpart of plant parasitic nematodes is a needlelike stylet which is used to puncture cells during feeding.
- There are two types of plant parasitic nematodes; Ectoparasitic nematodes which remain in the soil and feed at the root surface and Endoparasitic nematodes which enter roots and can live and feed within the root.
5. Nematodes as bioindicators of soil health or condition:
- Population of nematodes depends on condition of soil, climate, seasons, crops etc. Therefore indicates the condition of soil health.
- Analysis of the diversity and complexity of nematode communities in the soil is a valuable tool, which indicates soil biological fertility, or soil health.
6. Nematodes dispense microbes for infection:
- Nematodes carrying live and dormant microbes on their surfaces and in their digestive systems and help in distribution of bacteria and fungi throughout soil and also in rhizosphere region.
- Sometimes nematodes acts as a vector for plant viruses. Eg. Nepo viruses, Tobraviruses.
7. Human and animal pathogenic nematodes;
- Nematodes are pathogenic to animals and human.
- Eg. Ascaris,