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Symptoms
General Symptoms
The
plant parasitic nematodes are obligate parasites and except for a few
species attacking buds, stems, leaves or other above ground plant parts,
most of them feed on subterranean plant structures. Based on the mode
of feeding, they have been classified as ecto or endo-parasites.
Nematode-feeding on plant tissues may result either in mechanical or
biochemical injuries, which are directly or indirectly responsible for
symptom-manifestations of the disease. Mechanical injury occurs as a
result of continuous thursting of stylet into the cells of the host
plants while the biochemical type of injury is the resultant effect of
the release of nematode salivary juices in the plant cell. The process
of feeding is initiated by secretion of salivary juices into the plant
cell (through lumen of the stylet), which apparently facilitates
extra-corporeal food digestion necessary before it is injested into the
nematode body.
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Apart from
the assistance provided for food digestion, the salivary juices may
bring about alterations in the plant parts. For example, cell
division in the merismetic tissues may be stopped or slowed down or
the cells surrounding the stylet may exhibit hypertrophy or
hyperplasia or may die resulting in formation of lesions or necrotic
tissues. Both the mechanical as well as the biochemical injuries
manifest themselves in the form of specific morphological changes
in the plant (issues. The symptoms of injuries, caused by plant
parasitic nematodes can be divided, therefore, into two categories:
(1) above ground; and (2) below ground.
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