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

Nervous System

NERVOUS SYSTEM

• In general, nematodes have a highly developed nervous system.
• In plant parasitic nematodes, because of their small size, the only part visible in whole mounts is the nerve ring, the so called ‘brain’ of the nematodes.
• The nerve ring encircles the oesophagus, usually in the isthmus region, and hence is often referred as circum-oesophageal commissure.
• Six longitudinal nerves extend from the nerve ring anteriorly to innervate the cephalic sensory organs.
• Posteriorly, 4 main nerves-dorsal, ventral and 2 laterals arise from the nerve ring, run in the respective hypo dermal chords, and innervate various parts of the body.
• Transverse commissures inter-connect the longitudinal nerves throughout the body.

Associated with the nervous system are sense organs. (already covered in cuticle).

EXCRETORY - SECRETORY SYSTEM
Two types of excretory systems are present in nematodes- the Canalicular and the Glandular.

A. Canalicular type

• The longitudinal excretory canals/ tubes run almost the entire length of nematode body in the lateral hypodermal chords.
• These canals are interconnected and form a terminal excretory duct, which opens to outside through excretory pore, usually located in the oesophageal region on the ventral side.
• Most of the plant parasitic tylenchid nematodes have the canalicular type of system.
• Excretory duct is the only part visible in the whole mounts.

Figure 6.7 Types of secretory-excretory systems in nematodes

B. Glandular type

• This type of excretory system consists essentially of a single cell renette (sinus, ventral gland cell or cervical cell) which leads to an excretory duct that opens to the outside through a n excretory pore on the ventral side.
• The whole system lies freely in the pseudocoelom.
• Based on the type of excretory system, nematodes are divided into two taxonomic groups-Secernentea (having canalicular excretory system) and Adenophorea (having glandular excretory system).

Function:

• The exact function of the so called ‘excretory’ system is a matter of conjecture. The main nitrogenous waste materials are excreted by body wall and digestive system. Moreover, the ‘excretory’ system is known to ‘secrete’ gelatinous materials in certain nematodes (e.g. citrus nematode) in which eggs are deposited.
• It is also speculated that the ‘excretory’ system plays important role in osmo-regulation.
• Considering the diversity of functions performed by ‘excretory’ system, now-a-days, it is also referred excretory-secretory system.

RESPIRATORY AND CIRCULATORY SYSTEM

• The well-defined organs for respiration and circulation are lacking in nematodes. However, the systems do work. Oxygen required in the aerobic plant parasitic nematodes is believed to diffuse through the body cuticle.
• Pseudocoelomic fluid filled in the body cavity serves the function of circulatory system. The fluid is continuous throughout the body length and bathes the different organs.