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Nematodes are parasites belonging to animal kingdom that are of concerned in the agricultural crop health. They belong to phylum Nemata, previously named Nemathelminthes or Aschelmnthes, several hundreds of nematode species are known to feed on plants as parasites and cause a variety of diseases.

Most of the damage by nematodes is caused by secretion injected into plants while they feed. This secretion, called saliva, is produced in three glands, from where it flows into oesophagus and is injected through stylet. The males of species generally may not penetrate roots, but females invariably get established on roots and are responsible for destruction of the host. Nematode saliva liquefies contents of the cells of the host, making them easier to inject and assimilate. As the result of action of saliva, the host responses are expressed in disease symptoms such as hyrertrophy, hyperplasia, suppression of mitosis, cell necrosis and growth stimulation.

Plant pathogenic nematodes are permanent soil dwellers. They live freely in the soil and feed superficially on roots and underground steams. The integrated management of nematode diseases can be achieved by use of chemicals, cultural practices, biological control and host resistance.

Components of Integrated Management of Nematode Diseases

Chemicals:

There are numbers of chemicals having nematocidal properties which are categorized into fumigants and non-fumigants, chloropicrin, 1,3-D, EDB,DBCP and MIT are some of the nematicidal fumigants. Fumigants must be handled with great care because they may be toxic or even fatal if inhaled by human-beings. Ethoprop, Fensulfothion, Phenamiphos and Oxamyl are some of the non-fumigant chemicals used for nematode control by soil application through drenching. Nematocidal action of these fumigants is limited to narrow root zone only, and moreover they are highly toxic to mammals. Therefore chemical control of nematode did not progressed much in India. However, there is a evidence that chemical control would be economical if chemicals judiciously used on some cash crops such as cotton, sugarcane, tobacco, citrus, grapevine, potato and vegetables.

Cultural practices:

Several nematode species are crop specific for their feeding. Since nematodes are obligate parasites, the absence of susceptible hosts for 2 to 3 years may eliminate them. The potato cyst nematode Heteroderarostochiensis can be eliminated by cultivating maize, corn, beans or clover as a rotation crops for years. Meloidogyne spp.Can also be checked by growing non-host crops for two consecutive seasons. Crop rotation in some cases like Trichodorusis of no use since the nematodes have a very wide host range. Crop rotation with Tagetespatulaand T. erectais useful in majority of the nematodes, particularly Partylenchus, since their roots release some nematocidal compound

Nematode spread can be checked by uncontaminated nursery plant and keeping soil fallow to deprive them of roots on which they feed. Flooding lands results in death of some nematodes adopted to living in normal soil with ordinary moisture. Heat treatment may be given for killing nematodes within plant tissue before planting infested bulbs, tubers and roots or plants such as Chrysanthemum, Strawberries and Banana. Hot water treatment is given by soaking material in water at 52 to 55 0C for 10 min.

Biological control:

This strategy aims at increasing parasites and predators of nematodes in the soil. This is done by changing environment, adding organic amendments or introducing other organisms directly. Oil cakes of margosa, castor and peanut applied at 0.2% (W/S) 3 weeks before planting reduce infestation of Meloidogynejavanicaon okra and tomato.

Use of VAM fungi for avoiding damage caused by plant pathogenic nematodes can also be practiced. (Table 1).There are several nematophagous fungi that parasitize nematodes or their eggs of larvae.

 (Table 1 VAM fungi used for biological control of plant pathogenic nematodes)

Host

Mycorrhizal fungus

Plant parasitic nematode

Effect on host plant

Peanut

Gigospora margarita

Meloidogynehapla

Decrease in reproduction of nematode, increase in plant growth

Beans

Glomusetunicatus

M. javanica

Less disease damage and reproduction of nematodes

Cotton

Gigospora margarita

M. incognita

Decrease in damage to plant, decrease reproduction of nematode

Cutrus

Glomusfasciculatum

Tylenchussemipenetrans

Plant growth enhanced

Grapes

Glomusfasciculatum

M. arenaria

Growth stimulated

Such fungi have been categorized into three groups.

(a)  Predators that develop special nematode trapping structures (adhesive or non-adhesive) on the mycelium

(b)  Endoparasites, that produce adhesive or non-adhesive spores either adhere to surface of nematode or get infested by them

(c)  Parasites of root knot and cyst nematodes that attack eggs or females of these nematodes

Table 2. Control of nematode by fungal parasites

Nematode

Fungal parasites

Mechanism

Heteroderaschachtii

(beet cyst)

Catenariaauxiliaris

Trapping in sticky mycelium

Heteroderaavenae

(Cereals)

Nematopthoraheteroderae

Female parasites

Globoderarostochiensis

(Potato)

Phialophoraheteroderae

Cyst feeding

Ditylenchusdipsaci

Catenariaauxiliaris

Endoparasitism

Meloidogyne spp.

(Vegetables)

Dactylellaoviparasitica

Constrction rings

Meloidogynehapla

(Tomato)

Arthobotrysoligospora

Predation

Host resistance:

Cultivation of resistant varieties is perhaps the best strategy to achieve an easy and economical control of nematode disease. Varieties are available in several crops with resistance to Meloidogyne, Heterodere(Potato), Ditylenchusdipsaci(Oat), Rodopholus(Citrus) and Meloidogynegraminicola  (Rice; variety: TKM 6).


Authors:

Prof. Kedar V. Swami and Prof. Sevak A. Dhenge

Late R.G. Deshmukh College of Agriculture Tiwsa,

Dist.- AMRAVATI, State- MAHARASHTRA. 444903

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