Page 382 - e-Book

localized source of protein for nematode development. Plant parasite nematodes are notable

antagonists in the yields of crops in the agriculture system. It has been estimated that 10% of
world crop production is lost as a result of damage caused by plant-parasitic nematodes; this

represents one-third of the total loss attributed to pests and diseases (Whitehead, 1998).
Among the plant-parasitic nematodes, the root-knot nematode, Meloidogyne incognita is an

obligatory endoparasite that causes considerable damage to economically important crops
worldwide (Khan et al., 2004; Gogoi and Neog, 2003).

Root-knot nematode causes (a) quite different morphological and anatomical
responses in different plants and even in various parts of a particular plant and (b) different

species can cause different responses in the same plant (Krusberg, 1963). In addition, changes
in the physiology of plants when giant cell and galls are formed, contribute to reduced

growth. The nematodes influence cell response both by injecting oesophageal gland contents

and by feeding on the host cytoplasm, Details of biochemical changes in plant tissue infected
with root-knot nematodes are gradually accumulating.

In the diseased state the tissues disintegrate, growth and reproduction are affected and

water becomes deficient with altered biochemical constituents. All of these studies have
proved that the diseased state has a biochemistry of its own. It is suggested that (Roy, 1980)

one can evaluate the relationships of the host with the parasite by determining these

biochemical changes during infection, as it is evident that the extenses of damage to the host
and development of the parasite depend largely on these biochemical changes.

The pathogenicity of the root-knot nematode was recognized by Neal as early as1889.

The infection starts with penetration of the second stage juveniles (I2) root-knot nematode
Meloidogyne spp at the zone of elongation is the first step in establishing a host-parasite

association. It infects plant root in response to stimulus emanating from the roots (Green,

1971 and Prot, 1980).

The root exudates containing sugars, amino acids, electrolytes, etc., influence the
hatching of eggs and positive taxis towards growing root tips (Bird, 1959). The nature of

penetration of the nematode into the host plant has been studied by various workers

(Patel,1991; Siddiqui,1998).

Stunting is often associated with root tissue damage. The reduced roots grow due to
damage in the cortical system (Sujatha and Metha, 1998) and damage of xylem and phloem

372