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

General Characters of Plant Parasitic Nematodes

Nematology is the scientific discipline conventionally concerned with the study of phyto- nematodes which parasitize plants and are of economic importance to agriculture, horticulture and forestry.
Nematodes may be defined as bilaterally symmetrical, triploblastic, pseudocoelomic unsegmented invertebrates with four hypodermal chords, a tri-radiate oesophagus, circum oesophageal nerve ring and a definite tail but lack circulatory muscles and specialized organs for locomotion and respiration.
Nematodes belong to phylum Nematoda.
The cuticle of a typical plant-parasitic nematode is transparent, thus allowing the viewing of internal systems when viewed under the microscope, .

General Characters of plant parasitic nematodes

1. Plant parasitic nematodes in general are elongated, cylindrical, bilaterally symmetrical, unciliated worms with body tapering towards both the ends and having maximum diameter in mid body region. Variety of other shapes is also present, especially in sedentary semi-endoparasitic and endo-parasitic females which turn obese and acquire shapes other than normal cylindrical forms. Males, however, remain vermiform in all the genera of plant parasitic nematodes.
2. The body is covered by a transparent, tough, resistant cuticle that is secreted by a layer of hypodermal (epidermal) cells lying just beneath it.
3. Plant parasitic nematodes have a protrusible hypo-pharyngeal needle like knobbed stylet (spear) at the anterior end of the body, which is used to suck the cell cytoplasm from the host plants. Fungal feeding nematodes also possess stylet which may or may not be knobbed.
4. Nematodes possess a false body cavity or pseudocoelom i.e. a cavity lacking mesodermal lining internally or a cavity present between mesoderm and endoderm. Pseudocoelom is fluid filled and most part of it is occupied with intestine and components of reproductive system (Fig. 3.1).

Fig.3.1 Body Cavity

5. Oral aperture (mouth) is terminal and is surrounded by lips which contain sensory cephalic papillae. All other body openings like excretory pore, vulva and anus (in females) and cloacal aperture (in males)are ventrally located (Fig. 3.2).

Fig 3.2 Diagrammatic representation of nematode to show various body openings