| Severe occurrence of citrus root-knot disease was found in mountain area in Shunchang county, Fujian province. Symptom characteristics of the citrus root-knot disease have been described in detail. Morphological characteristics, electrophoretic phenotypes of esterase (Est) and malate dehydrogenase (Mdh), host range test, molecular characterization demonstrated that this nematode species differs cleanly from other previously descried roo-knot nematodes. The species of the root-knot nematode was described in provisional as Meloidogyne shunchangensis n. sp., the species epithet referring to the locality of the nematode. The other parasitic nematodes of citrus roots were also identified.Meloidogyne shunchangensis can infect Poncirus trifoliate. The characteristics of root galls on roots produced by M. shunchangensis were that compound galls along the axes and at the tips of fibrous roots, lateral roots can developed in root-knot and can also been infected by M. shunchangensis. In the host-rnage test, soybean, peanut, tobacco were not host of Meloidogyne shunchangensis. Cowpea, cucumber, tomato, pepper were mildly infected by Meloidogyne shunchangensis. The small root galls on roots of these host were along the axes of roots, lateral roots can developed in root-knot.The perineal pattern of the female vary from circular to ovoid with a moderately high dorsal arch and with rounded and finely spaced striaetions. The centre of origin of striae is on tail tip region. There is no striae or few striae between vulva and anus, and s distince fold below the anus. Phasmids are large, distint, round, situated a little wider apart than the length of vulval slit. There is a range of variation on lateral fields which is without lateral lines or with a single or double iner lateral lines on one side or both sides of lateral field. Labial disc of female slightly raised above medial lips. Medial lips indented medially , and dividing into lip pairs. Lateral lips are large, squarish. Extretory pore located posterior to atylet base, which EP/ST ratio is 2.7. Labial disc of male fused with medial lips to form dumbbell-shaped lip structure. There are on annulations on head region of male. Lateral field at middle body marked by four incisures and a retuse line on middle ridge, areolations on outer bands. Relatively short Second-stage juvenile's body length , 332.7μm long with fairly long stylet about 13.4μm of mean length, short tail, 24.2μm long in mean value, ending in a broad terminus, with a short hyaline region 4.3μm.The isozyme electrophoretic analysis of young egg-laying females of M. shunchangensis n.sp. revealed Mdh-Est Phenotype is a new phenotyee, which one stong malate dehydrogenase (Mdh) band at Rm 37.9%, a weak Mdh band at Rm 23.7%, and a esterase (Est) band at Rm 55.7%.The ITS regions , D2-D3 region of 28S rDNA of M. shunchangensis n.sp. were amplified, cloned and sequenced. The ITS, D2-D3 sequences of M. shunchangensis n.sp.were clearly different from other root-knot nematode that present in the GenBank database. The percent identity of M. shunchangensis n.sp.with other species of root-knot were 75%- 81% based on the sequences of ITS1-5.8S-ITS2, 79%- 84% based on the sequences of D2-D3. Phylogenetic trees derived from Neighbor-Joining (NJ) analysis based on ITS1-5.8S-ITS2 and D2-D3 showed that M. shunchangensis n.sp. can be differentiated from other root-knot nematode species described.Nine genera and six species of nematodes were identified from the roots and rhizosphere soil of citrus which were infested with citrus root-knot nematode. The six species of nematodes were Helicotylenchus pseudorobustus, Hemicriconemoides minor,Paratylenchus bukowinensis,Xiphinema americanum group,Xiphinema hunaniens. The population structures of nematodes in rhizosphere of citrus were also preliminary analysis.
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