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Introduction:

The word Nematode is derived from the Greek word, what is the word?. Meaning “thread like ones” (nema means “thread” and ode means “like”). Nematodes can therefore be described as thread-like worms. (dropking 2001). Nematodes, eelworms and round worms are synonymous for the same group of organisms. The Phylum Nemata, to which nematodes belong occupies an intermediate position between the Phyla Platy helminthes (these include flukes and tapeworms) and Annelida (which include the common earthworms) (Duncaa, 200).

A number of genera and species of nematodes are highly damaging to a great range of hosts, including foliage plants, agronomic and vegetable crops, fruit and nut trees, turfgrass, and forest trees. Some of the most damaging nematodes are: Root Knot (meloidogyne spp.); Cyst (Heterodera and Globodera spp).; Root lesion (pratylenchus spp.); Spiral ( Helicotylenchus spp.); Burrowing (Radopholus similis);Bulb and stem (Ditylenchus dipsaci); Reniform (Rotylenchulus reniformis); Dagger (xiphinema spp.); and Bud and leaf (Alphelenchoides spp.)

Nematodes are simple, multi-cellular animals-typically containing 1,000 cells. They are worm-like in appearance but are taxonomically distinct from earthworms, wireworms, or flatworms, they are bilaterally symmetrical, soft-bodied (no skeleton) non-segmented round worms. Most nematodes species that attack plants are microscope. The basic body plan of nematodes is a “tube within a tube.” Most nematodes are not pathogens but rather saprophytes. Some, however, are serious human, animals, and plant pathogens. Those that attack animals or humans do not attack plant and vice versa. Heartworm in dogs and cats and elephantiasis in humans are examples of nematode disease in animals and people.

Plant parasitic nematodes may attack the roots, stem, foliage, and flowers of plant. All plant parasitic nematodes have piercing mouthparts called stylets. The presence of a stylet is the key diagnostic sign differentiating plant parasitic nematodes from all other types of nematodes. The bacterial-feeding nematodes, Caenorhabditis elegans, is one of the best-understood animals on earth. It was the first animal to be completely sequenced. The study of C. elegans has led to many new insights into animal development, neurobiology, and behavior.

Typical root symptoms indicating nematode attack are root knots or galls, root lesions, excessive root branching, injured root tips, and stunted root systems. Symptoms on the above ground plant parts indicating root infection are a slow decline of the entire plants, wilting even with ample soil moisture, foliage yellowing, and fewer and smaller leaves. These are, in fact, the symptoms that would appear in plant deprived of a properly functioning root system. Bulb and stem nematodes produce stem swellings and shortened internodes. Bud and leaf nematodes distort and kill bud and leaf tissue.

Parasitic nematodes are readily spread by physical means that can move soil particles about equipment, tools, shoes, birds, insects, dust, wind, and water. In addition, the movement of nematode infested plant or plant parts will spread the parasites. (Elis et al, 2008).

Nematodes have been known as pests of man since the dawn of medicine. Nematodes are the most highly developed of the pseudo coelocates. They are widely present in the soil, fresh water and marine water. Nematodes are the only plants parasites belonging to the animal kingdom which are studied in plant pathology. Nematodes are worm-like in appearance but quite distinct taxonomically from the true worms. Numerous species of nematodes attack and parasitize man and other animal’s and cause various diseases. Several hundred species are known to feed on living plants as parasites and cause a variety of plant disease. Crofton (2004) gave a general account of Nematodes. Wallace (1963) published one of the most interesting works on the xbiology xof plant parasitic nematodes. Swarup and Seshadri (1974) reviewednematology in india. Plant Nematology is primarily a study of nematodes associated with plant life, although many investigators includes those forms found in the soil and water. As often stated, Nematodes can be found anywhere life exist. (Singh, 2001).

Nematodes are usually regarded as being microscopic in size through a few species can be seen without magnification. Most plant parasitic nematodes would range in size from 0.02 to 0.04 inches in length. As the common name eel worm implies, a great number of nematodes have a worm like or eel-like shape. The females of some kinds grow swollen at maturity and resemble tiny beans, lemons or pears.

Nematodes commonly have six developmental phases including an egg, four juvenile stages and an adult nematode stage. Each juvenile stage is complicated by a developmental process called a molt. Except for size, juveniles usually resemble adults. Reproductive organs normally do not appear until after the nematodes have under gone molts (Mai, 1999).

Nematodes that effect plant growth are called plant parasitic nematodes and are classified according to their feeding behavior. Migratory ectoparasites feed from outside the root moving from cell to cell and piercing them to feed without entering root tissue. For example, Dagger nematodes, xiphixnema, spp. Sedentary ectoparasites unnel partially into roots, their heads entering to establish permanent feeding sites, while their bodies remain outside the plant; for example, citrus nematode, Tylenchulus, Semipenetrans (Abawi, 1994).

Migratory nematode endoparasites feeds inside root, tunneling inside and moving back into soil and to new roots at will; for example: rot leision nematodes, pratylenchus, spp. Sedentary endoparasites yunel into the roots establishing permanent feeding sites from which they do not move. They may protrude from the roots as they grow, example include root knot nematodes Meloidegyne spp and cyct nematodes, Heterodera spp. Nematodes that attack above ground portion of plant may be either ectopasites or endoparasites at different point in their life histories (Abawi, 1994).

Plant are living organisms belonging to the kingdom plantae. They include familiar organisms such as trees, herbs, bushes, grasses, ferns, mosses, and green algae. Some plant such as pearl millet, sorghum, corn or maize and pigeon pea are found to be susceptible to nematode infestation. They are mostly found to be parasitized by fungi and bacteria. This is as a result of the nature of these plants. Most of these plants are very rich in protein and can convert atmospheric nitrogen to nitrates which they absorb (Idodo, 2004).

1.1 STATEMENT OF THE PROBLEM

There are many damages like root knot of vegetable caused by plant parasitic nematodes in all villages in Nigeria. As a result of nematode infection on many plants, there is a great yield loss.

1.2 BASIC ASSUPMTION:

From the ideology of people about the effect of nematode diseases on plants. The following assumptions are madel:

1. Nematode pest must be present in the soil to cause infections

2. Nematodes can be prevented from entering in to the soil.

3. Nematodes are classified based on the diseases they cause.

1.3 OBJECTIVES OFF THE STUDY

The study is intended to:

1. Find out some plant diseases caused by nematodes.

2. Determine the effect of nematode diseases on plants.

3. Find such on to the problem caused by nematode infections.

1.4 JUSTIFICATION OF THE STUDY

It was observed that there have been a large number of yield losses as a result of nematode infection on plant in many counties of the world including Nigeria.

However, the essence of the study is to provide the needed information on the effect of nematode diseases on plants and also information on how to control these nematode diseases. The study is justified because it will produce result which will help scientist to conduct further research that may contribute to a comprehensive agricultural policy in the country.