Nematoda

Define Nematode

Nematodes are a group of worms. They occur naturally and are very hard to detect visually. These are common soil pests that affect plants. The soil at low levels contains numerous Nematodes. Nematodes can enter the farm through infected transplants. They are parasites of both plants and animals and attack the insects also. However, they cause severe damage to plants. But not all Nematodes are harmful to the plants. Some play an essential role in nutrient recycling.


Commonly known as roundworms, they are unsegmented vermiform pests. They are free-living organisms. Sometimes they enter the plant to extract nutrients from the root cell. They stress tolerance of the plant. Plants abundant with water and nutrients help can tolerate nematode attacks. Once they are present in the soil, It is almost impossible to eliminate. 


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Characteristics of Nematoda

Following are the Nematodes Characteristics

  1. Tubular in appearance. It has an elongated and thin body (hair-like).

  2. The alimentary canal is distinct, but the head and tail are not visually different.

  3. Majority of these are tiny and can be microscopic. 

  4. They are free-living organisms. 

  5. They reproduce sexually. They produce amoeboid sperm cells.

  6. They have a nervous system. 

  7. They are parasites of both plants and animals.

  8. They have cuticles that moult periodically.


Classification of Nematodes 

Approximately 15000 species of Nematoda have been identified till now. Some nematodes live in the roots of plants; some spend their life inside the plants. These are not plant-specific. Following are the main three classes of Nematodes that has been classified further in subclasses and subclasses: 

  1. Kingdom Animalia 

  2. Phylum Nematoda -

I. Class Rhabditea -

(i) Parasite Rhabditea (ii) Free-Living Rhabditea (iii) Rhabditis (iv) Tylenachia

II. Class Enoplea 

(i) Enoplia (ii) Dorylaimia

III. Class Chromadorea

(i) Chrimadoria


1. Kingdom - Animalia

Nematodes are multicellular eukaryotic organisms like other organisms (animals, plants, most algae, fungi, Metazoa, and protists) in kingdom Animalia. Their cells contain a nucleus and other organelles. They obtain nutrients from organic sources, just like other organisms.


2. Phylum - Nematoda

Nematodes, also known as roundworms, make up the phylum Nematoda. 


Phylum Nematoda Classification

Phylum Nematodes are further classified into three major classes and subclasses:


I. Class Rhabditea

Class Rhabditea has both free-living and parasitic nematodes. The majority is of parasite nematodes in this class. Rhabditea Free-living feeds on bacteria as a source of energy. They can be found in between soil particles as well as in water. 


General Characteristics of Rhabditea

  • They are unsegmented. 

  • They Possess a cylindrical body. 

  • They are tapered at either end 

  • They possess a cuticle and hypodermis 

  • Adult species have intestine, gonads and pharynx. 

  • They have invaginated cuticles with nerves


Rhabditea is Further Classified Into Two Subclasses: 

(i). Parasitic Rhabditea

Parasitic Rhabditea nematodes examples are Ascaris species, Enterobius species (e.g. human pinworm), Necator as well as Wuchereria species. These species cause many serious diseases in human beings. This species is common in the tropics.


(ii). Free-Living Rhabditea Nematodes

They are found in temperate environments. They live in bacteria-rich habitats such as compost to obtain nutrients. They depend on other insects for transport from one location to another. Caenorhabditis Elegans worm is the best example of Free-Living Rhabditea Nematodes. 


Further Classification is as Follows:

(i.a.) Rhabditis - They have well-developed Phasmids and poorly developed invaginated cuticles with nerves called aphids.

(i.b.) Tylenchia - Found in plants often in the form of parasites.


(II). Class Enoplea

Enoplea makes up the phylum Nematoda. These ancestrally diverge nematodes. Some of Enoplea nematodes examples are Trichuris, Diotyphyme, and Diotyphyme.


Enoplea Nematodes Characteristics:

  • Cylindrical or bottle-shaped oesophagus.

  • Well-developed Amphids

  • The simple excretory system made up of a few ventral or glandular cells

  • Do not live in marine environments 

  • Possess teeth-like structures


Subclasses of Enoplea Nematodes

(i) Enoplia - They have oval or pouch-like amphids, cylindrical oesophagus, and smooth body. 

(ii) Dorylaimida - Majority of this species is a free-living organism. They can be predators or omnivorous. Some, like Trichinella, exist as parasites. 

IIII. Class Chromadorea

This class can be found in a broader range of habitats as it consists of about four distinct lineages. This class also has both free-living and parasitic members. Chromadorea is smaller in size. But they are higher in number in their habitats as they reproduce at a higher rate.


Characteristics

  • Three esophageal glands,

  • Spiral aphids

  • Pore-like amphid of Chromadorea

  • Possess annulated cuticles

  • Glandular of tubular excretory systems 

Sub-class: (i) Chromadoria

Control Nematoda

The infected plants by nematodes cannot grow well, are paler than normal, often dwarfed, may wilt in the heat of the day, small leaves. These symptoms can be misunderstood with symptoms of nutrient deficiency. It has been noticed that infected plants can look healthy while growing in fertile soil, or during cool weather.


Growth of plants with nematodes will lead to a larger population of it. Try to inspect the roots of plants before placing them into the farm. Because if nematodes are present in the soil, they are almost impossible to abolish altogether, but the damage to plants due to them can be reduced.

FAQ (Frequently Asked Questions)

Question 1: How can the Damage to Plants Due to Nematode Attack can be Reduced?

Answer: The following practices can reduce damage to plants due to nematode attack:

  1. Chemical Nematicides to reduce the damage to plants.

  2. Cultural practices to lower the nematode level.

  3. Crop rotation to reduce nematode level in the soil. Many nematode-resistant plant varieties are now available.

  4. Early-season cropping/late-season plantings can avoid serious nematode damage due to reproduction. 

  5. Root destruction to avoid nematode feed on and reproduce in the root in the soil.

  6. Increased water and nutrients will surely help plants to reduce damage due to nematode attack. 

  7. Soil Solarisation. The high temperature will help to control nematodes.

Question 2. Are all Nematodes Parasites?

Answer: 40% of the nematodes are free living and usually feed on bacteria, protozoa, fungi and other 40% of the nematode parasites. Most nematodes are parasites on animals (44% of the species -invertebrates and vertebrates. Also 15% of the species is on plants.