Nematode Pests of Horticultural Crops and their Management (1+1)

Body Organization

The nematodes body is tubular. It consists of two tubes.

• Outer body tube - Wider, larger, represents the body wall.
• Inner body tube - Smaller, narrower, represents the Alimentary canal.The two tubes join anteriorly to form lip region and are posteriorly connected through rectum.
  

Figure 5.1 Tubular body organization

The outer body tube ( body wall) consists of three layers:

• Cuticle
• Epidermis (Hypodermis)
• Somatic Musculature (muscles of body wall)
  

Cuticle:

• It is a non-cellular, non-living, tough but elastic, multilayered external covering secreted by hypodermal cells that acts as an exoskeleton and protects the inner soft body tissue.
• Apart from covering the body externally, the cuticle invaginates in to the body at oral aperture, excretory pore, vulva, anus etc., and lines the alimentary canal, excretory duct, vagina, rectum/ cloaca and some sensory structures.
• The cuticle covering the body is called external cuticle and that lining the internal structures is called internal cuticle.
• Tail region of the males of most of the plant parasitic nematodes bears a wing like lateral cuticular extension known as bursa (Caudal alae) which helps to clasp the females during mating.

Functions

1. Cuticle along with hypodermis forms the exoskeleton of nematodes. It prevents radial deformation of the body during undulatory motion caused by the longitudenal muscles.
   
2. Being elastic, it maintains turgor pressure of the body.
3. Being selectively permeable, it acts as a barrier to harmful elements in the environment and plays a role in uptake of the substances.l It allows the transport of gases,.
4. Cuticle is the seat of many sensory structures.
5. Longitudinal alae of the cuticle assist in locomotion.
6. It supports the musculature.

Hypodermis:

• It is made up of a single layer of cells or some times syncytial in nature which lies between the cuticle and musculature.
• While basically it is a thin layer, it thickens characteristically in dorsal, ventral and lateral positions to form four longitudinal chords (one dorsal, one ventral and two lateral chords) of which lateral chords are more conspicuous.

Figure 5.2 Cross section of nematode to show the body layers Courtesy :nematodexs.gif

Functions

1. Hypodermis secretes and maintains the cuticle.
2. It accumulates proteins and nucleic acids at the time of moulting.
3. Hypodermal glands act as osmotic and ionic regulators.

Somatic musculature:

• Somatic muscle cells are arranged longitudenally beneath the hypodermis in the four inter-chordal zones just beneath the hypodermis.
  
• In addition, there are some specialized muscle cells that are attached to specific organs like stylet, spicule etc. to enable these organs to make specific movements.

A muscle cell comprises of two distinct zones;

1. Contractile fibrillar zone that contains myofibrils
2. Non-contractile sarcoplasmic zone that contains nucleus and cytoplasm.

Types of muscles in nematodes
Muscle cells have been differentiated in to three types on the basis of their shape and arrangement of contractile fibres.
Platymyarian muscles: Wide flat-base with contractile fibres limited to the base lying closest to the hypodermis. Present in smaller nematodes like plant parasitic forms.
Coelomyarian muscles: Narrow base with contractile fibres extending up the sides of the muscle cells. More common in large nematodes
Circomyarian muscles: Round muscles with contractile fibres all along its circumference. (Rare; found in the stylet, vulva & spicules etc.)

Platymyarian muscle

Coelomyarian muscle Circomyarian muscle

Figure 5.2 Types of muscles in nematodes

Two types of muscle arrangement is usually observed.

• Meromyarian having two to five muscles in each inter-chordal zone.
• Polymyarian having more than five muscles in each inter-chordal zone.

Platymyrian muscle cells are meromyarian and coelomyarian muscle cells are polymyarian in arrangement.
Functions

1. Musculature helps in locomotion and other movements specific of organs.
2. They also act as reservoirs of the stored food material.