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Xiphinema americanum
''Xiphinema americanum'' (American dagger nematode) is a plant pathogenic nematode. It is one of many species that belongs to the genus ''Xiphinema''. It was first described by N. A. Cobb in 1913, who found it on both sides of the United States on the roots of grass, corn, and citrus trees.〔Cobb, N. A. (1913). "New nematode genera found inhabiting freshwater and non-brackish soils.". J. Wash. Acad. Sci. 3: 432-435.4〕 Not only is ''Xiphinema americanum'' known to vector plant viruses, but also ''X. americanum'' has been referred to as "the most destructive plant parasitic nematode in America", and one of the four major nematode pests in the Southeastern United States.〔Christie, J. R. (1952). "Some new nematodes of critical importance to Florida growers.". Proc. Soil Sci. Soc. Fla. 30: 39〕〔Thorne, G. (1961). "Principles of Nematology". McGraw-Hill. New York. 553p〕〔Wang, S., Gergerich, R., Wickizer, S., Kim, K. (2002). "Localization of transmissible and nontransmissible viruses in the vector nematode Xiphinema Americanum". Phytopathology. 92: 646-653〕
==Morphology and anatomy==
The length of the adult ''Xiphinema americanum'' ranges from 1.3 to 3.0 millimeters. The dagger nematode is characterized by a 100 μm odontostyle which is used for deep penetration of root tips with its spear-like stylet. The odontostyle is connected to the lining of the cheilostome by a folded membrane called the "guiding ring". The guiding ring is attached to a flanged odontophore.〔
Females: The body is usually in an "open C" conformation. The shape of the body tapers towards the extremities. The two rings of the odontophore are located 3 μm apart. The ''Xiphinema americanum'' esophagus is dorylaimoid with an enlarged posterior portion that occupies roughly 1/3 of its total length. The esophagus contains a muscular bulb which is 80 μm long and 20 μm wide. The valve between the esophagus and the intestine is (amorphous ).〔Lamberti, F.; Golden, M. (1984). "Redescription of Xiphinema americanum Cobb, 1913 with comments on its morphometric variation". Journal of Nematology 16(2): 204-206.〕 The (vulva ) is 46-54% of the total body length, and is located equatorially with a transverse slit shape, with the (vagina ) having a diameter of 1/3 of the body diameter.〔 The ovaries normally occur in pairs, and are amphidelphic and relexed. The prerectum of ''X. americanum'' measures 120-140 μm long, with a (rectum ) that is roughly the same length as the body diameter at the anus. The tail contains 2-3 pairs of caudal pores, is conoid, and curves dorsally with a subacute terminus.〔
Males: The males have a similar overall configuration as the females, but are slightly smaller in length. Males of ''X. americanum'', however, are rarely found in nature. The male has diorchic (testes ) that are connected to the cloaca, with one anterior branch and one posterior branch.〔 It is common to find more coil in the posterior region.〔 The males also have paired spicules but lack a gubernaculum and bursa.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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