First report of Xiphinema hunaniense Wang & Wu, 1992 (Nematoda: Longidoridae) in Vietnam

Eight females: L = 2,095 ± 130 (1,947-2,189) µm, V% = 24.7 ± 0.4 (24.2-25), Odontostyle = 126 ± 5 (120-130) µm, Odontophore = 71 ± 1 (70-71) µm, Stylet = 196 ± 6 (190-201) µm, Tail length = 45 ± 1 (44-46) µm, Lip width = 13.6 ± 0.1 (13.5-13.7) µm, Lip height = 5.4 ± 0.2 (5.2-5.6) µm, Pharynx = 359 ± 3 (356-361) µm, Anterior end to guiding ring = 121 ± 7 (114-127) µm, Width at pharyngo-intestinal junction = 44 ± 1 (43-44) µm, Width at mid-body = 46 ± 1 (45-47) µm, Width at anus = 29 ± 2 (27-31) µm, a = 46 ± 2 (43-48), b = 5.8 ± 0.4 (5.4-6.1), c = 46 ± 4 (42-49), c′ = 1.6 ± 0.1 (1.5-1.7).

The females of the Vietnamese population of X. hunaniense is characterized by an offset lip region from body contour, lack of anterior genital branch, vagina directed slightly backward, and a digitate tail (Fig. 1). Morphology and morphometrics of this population are highly similar to the type population of X. hunaniense except for smaller a value (43-48 vs 51-57), c value (42-49 vs 53-63), longer stylet (190-201 µm vs 180-187 µm), wider width at pharyngo-intestinal junction (43-44 µm vs 21-23 µm). However, these morphometric variations have been reported from other populations of X. hunaniense (Luc, 1981; Wu et al., 2007; Long et al., 2014). Two 28S rDNA sequences (1 bp difference) of the Vietnamese population of X. hunaniense were obtained, 942 to 944 bp long. These sequences are 98.9 to 99.5% similar (3-8 bp difference) to 28S rDNA sequences of X. hunaniense from other populations. The Bayesian inference phylogenetic tree showed that 28S rDNA sequences of the Vietnamese population of X. hunaniense were placed together with sequences of X. hunaniense from other populations (100% PP) and this group has a sister relationship (73% PP) to the sequences of X. brasiliense (Fig. 2).

When it comes to morphology, X. hunaniense is closest to X. radicicola, and therefore, it has been synonymized with X. radicicola by Loof et al. (1996). However, based on the observation of different populations of X. hunaniense and X. radicicola, Robbins and Wang (1998) re-established X. hunaniense as a valid species that was agreed by Zheng and Brown (1999). 28S rDNA sequences of X. hunaniense has a sister relationship to X. brasiliense, but X. hunaniense can be differentiated from X. brasiliense by the moderately offset terminal peg vs distinct peg-shaped tail and X. brasiliense usually has more posterior vulva position. Besides, the 28S rDNA sequences of X. hunaniense from Vietnam were only 87 to 88% similar (84-85 bp difference) to X. brasiliense.

Due to the conserved morphology in some Xiphinema species groups, i.e. X. hunaniense – X. radicicola – X. brasiliense (Zheng and Brown, 1999) or X. americanum group (Gutiérrez-Gutiérrez et al., 2012), the combination of morphological characters and molecular data is needed to identify Xiphinema species. This is the first report of X. hunaniense in Vietnam with the support of molecular data of 28S rDNA sequences, adding to the total number of nine Xiphinema species in Vietnam, including X. americanum, X. brasiliense, X. brevicolle, X. diffusum, X. elongatum, X. insigne, X. longicaudatum, X. radicicola, and X. hunanie nse.

Figure 1:

Figure 2: