The existence of nematodes known for 4 billion years has contributed for their rich biodiversity, prevalence, occurrence and distribution under varied agro-eco-systems.-parasitic nematodes are of great economic However, because most of them live in the soil, they represent one of the most difficult pest problems to identify, demonstrate and control. Their effects are commonly underestimated by farmers, agronomists and pest management consultants, but it has been estimated that some 10 percent of world crop production is lost as a result of plant nematode damage . plants represent a taxonomically heterogeneous assemblage of angiosperms that rely partially or completely on host plants for organic, inorganic and water resources. Plant-parasitic nematodes are recognized as one of the greatest threat to crops throughout the world. exist in a complex and dynamic relationship between host, environment, edaphic and biotic factors and are common in many natural and semi-natural ecosystems from tropical rain forests to the high Arctic. Of the known parasitic angiosperms, about 25 genera negatively affect host plants cultivated by humans and out of these Striga, Orobanche, Loranthus, Dendrophthoe, Viscum and Cuscuta are considered agronomically important and much research has been undertaken on these parasitic genera. Among these, Cuscuta species (dodders) are the best known .The parasitic relationship of Cuscuta with its hosts has been the subject of numerous investigations. Host morphology and phenology are considered as the two primary factors which are responsible for selection of different hosts by Cuscuta specie.A parasitic plant is a plant that derives some or all of its nutritional requirements from another living plant. All parasitic plants have modified roots, named haustoria (singular: haustorium), which penetrate the host plants, connecting them to the conductive system – either the xylem, the phloem, or both. This provides them with the ability to extract water and nutrients from the host. Some parasitic plants are able to locate their host plants by detecting chemicals in the air or soil given off by host shoots or roots, respectively. About 4,100 species of parasitic plant in approximately 19 families of flowering plants are known.
Although tiny, parasitic plant nematodes are mighty. It is estimated that
nematodes cause $85 billion dollars of crop losses worldwide each year. Since
parasitic nematodes are microscopic and below the soil surface, above-ground
symptoms can often be misdiagnosed
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