Xiphinema

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Dagger nematodes
Scientific classification
Kingdom: Animalia
Phylum: Nematoda
Class: Enoplea
Subclass: Dorylaimia
Order: Dorylaimida
Suborder: Dorylaimina
Superfamily: Dorylaimoidea
Family: Longidoridae
Genus: Xiphinema
Cobb, 1913
Species

See text.

The Xiphinema genus respresents ectoparasitic root nematodes commonly known as the Dagger nematode.[1] The major species are X.americanum, X.diversicaudatum, X.index, X.italiae and X.pachtaicum.[2] The genus is of economic importance on grape, strawberry, hops and a few other crops. They are easily recognizable, due to a long body length and a long stylet capable of reaching vascular tissue.[3] Different members of the genus have been shown to induce moderate to large amounts of root damage through root penetration, which in some species results in the formation of galls.[2] They are most feared because of their capability to act indirectly as virus vectors of various nepoviruses. The virus is often vectored by specific species and attaches to the interior cuticle lining where it can be transferred from infected to uninfected root tissue as the nematode feeds and sheds.[4] Efforts to study these nematodes in more detail have proved problematic in some species due to difficulties in maintaining populations in a greenhouse environment.[3]

Morphology[edit]

Xiphinema are large nematodes, with an adult length between 1.5mm – 5.0mm. .[1] They have a long protrusible odontostyle, with 3 basal flanges at the posterior end of the stylet and a relatively posterior guiding ring when compared to the genus Longidorus.[3] The odontostyle is lined with cuticle and alongside the esophagus serves as a good surface for viruses such as arabis mosaic virus to form a monolayer, which can be vectored to healthy plants.[4] Xiphinema have a two-part esophagus, which does not contain a metacorpus. A modification in the posterior end of the esophagus forms a muscular posterior bulb, which can generate a pumping action similar to that of a metacorpus in other plant parasitic nematodes.[4] The number of males varies from abundant to sparse depending on the species. .[1] Males have paired spicules but the gubernaculum and bursa are absent. Males of different species can be characterized using the varying number and arrangement of papillae.[3] Females could have 1 or 2 ovaries.[3]

Taxonomy[edit]

There are 296 nominal taxa, including 234 accepted species, 49 synonyms and 13 species inquirendae.(He 2003)

History[edit]

Xiphinema americanum was the first species to be described by Nathan Cobb in 1913, who speculated that it was likely a plant pathogen. .[1] This speculation was experimentally confirmed in 1949 and 1952.[5]

List of species[edit]

N.B. This list is probably incomplete.

Distribution[edit]

The Xiphinema genus is distributed worldwide. Two economically important Xiphinema species; X.index and X.americanum are both commonly found in California and tend to be problematic in vineyards. Xiphinema diversicaudatum is also found in parts of the U.S, as well as Europe and Australia.[3]

Life Cycle and Reproduction[edit]

Eggs are laid singly in thin water layers in the soil and are not part of an egg mass. After the first-stage juvenile emerges from the egg there are 3 or 4 molts, all of which occur in the soil.[3] Males can be abundant or sparse depending on the species, which may suggest the presence of both parthenogenic and amphimitic species.[3]

Host Parasite Relationship[edit]

Xiphinema has a very wide host range including crops of high economic importance such as grape, hops and strawberry. Other documented hosts include: Nectarine, oak, rose, grapevine, raspberry, carrot, cherry, peach, and soybean.[3]

References[edit]

  1. ^ a b c d Whitehead, A.G. 1998. Plant Nematode Control
  2. ^ a b Evans, K., Trudgill, D.L., Webster, J.M. 1998. Plant Parasitic Nematodes in Temperate Agriculture.
  3. ^ a b c d e f g h i Xiphinema at Nemaplex, University of California
  4. ^ a b c Taylor, C.E., Robertson, W.M., 1970. Sites of Virus Retention in the Alimentary Tract of the Nematode Vectors, Xiphinema diversicaudatum (Micol.) and X.index (Thorne and Allen), Annals of Applied Biology (1970),66, 375-380)
  5. ^ Schindler, A.F., 1957. Parasitism and Pathogenicity of Xiphinema diversicaudatum, and ectoparasitic nematode. Nematologica, II (1957):25-31)

Bibliography[edit]