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First Report of Plant-Parasitic Nematode Meloidoderita salina in the Netherlands

After the description of the root-parasitic nematode Meloidoderita salina from a tidal salt marsh in France (1), an additional sampling was carried out to search for the presence of this unusual nematode in a tidal salt marsh area close to Sint-Annaland, Zeeland Province, the Netherlands. In August and October 2012, a total of 25 soil and root samples were collected from the halophytic plants Atriplex portulacoides L. (so far the only known host for this nematode species), A. littoralis L., A. prostrata Boucher ex DC., Limonium vulgare Mill., Salicornia europaea L., Aster tripolium L., and Plantago maritima L. All these halophytes grow in a cohesive muddy soil type within the salt marsh, except A. littoralis and A. prostrata, which grow in the litter tidal zones on the edges of this area. Nematodes from roots and soil were extracted by centrifugal flotation (2) and Oostenbrink's cotton-wool filter methods (4), respectively. Additionally, roots were used for direct observation of females and young cystoids with a dissecting microscope. Finally, all stages were compared morphologically with available type material (1). Root and soil samples demonstrated that only nematodes isolated from A. portulacoides, A. littoralis, and A. prostrata contained all life stages of the genus Meloidoderita, while on the roots of L. vulgare, S. europaea, A. tripolium, and P. maritima, no Meloidoderita was observed. The soil samples included males, cystoids, and second-stage juveniles (J2) in low densities (<20 nematodes/100 ml), while swollen females and young cystoids were observed on root samples. All stages (n = 10 per life stage) fit morphologically with the recently described M. salina. Females were swollen with an oval to pear shaped body with a small posterior protuberance, irregular and twisted neck, oval and backwardly sloping stylet knobs, a prominent secretory-excretory (S-E) pore with cuticular lobes, and a swollen uterus with a thick hyaline wall. Males were without stylet, strongly sclerotized S-E duct, and tail tapering to rounded terminus ending in one or two ventrally terminal mucron. J2s had a well-developed stylet and rounded knobs set off from shaft and conical tail slightly curved ventrally and tapering to a finely pointed terminus with a finger-like projection. Cystoids showing the unique sub-cuticular hexagonal beaded pattern (1). J2s were also used for molecular analysis. DNA was extracted by incubating individual J2s in a lysis buffer as described in (3). Two primer combinations were used to amplify the small subunit ribosomal DNA (SSU rDNA) from a 100-times-diluted crude lysate (two overlapping fragments, [3]). The resulting (nearly) full-length SSU-rDNA sequences (GenBank KF751617 and KF751618) showed >99% identity with M. salina sequences from nematodes collected in the aforementioned tidal salt marsh in France (FJ969126 and FJ969127). To our knowledge, this is the first report of M. salina in the Netherlands. Moreover, this is the first record of M. salina parasitizing A. littoralis and A. prostrata. Although these Atriplex species are used for human consumption, the effect of M. salina on the host is unknown so far.

References: (1) S. Ashrafi et al. Zookeys 249:1, 2012. (2) W. A. Coolen. Pages 317-329 in: Root-knot nematodes (Meloidogyne species). Systematics, biology and control. Academic Press, New York, 1979. (3) Holterman et al. Mol. Biol. Evol. 23:1792, 2006. (4) M. Oostenbrink. Pages 85-102 in: Nematology. University of North Carolina Press, Chapel Hill, 1960.