Longidorus cheni, Barsalote, Eda Marie, Pham, Hoa Thi, Lazarova, Stela, Peneva, Vlada & Zheng, Jingwu, 2018

Barsalote, Eda Marie, Pham, Hoa Thi, Lazarova, Stela, Peneva, Vlada & Zheng, Jingwu, 2018, Description of Longidoruscheni sp. n. (Nematoda, Longidoridae) from China, ZooKeys 744, pp. 1-18 : 2-6

Longidorus cheni sp. n. Figures 1, 2, 3, 4, 5

Material examined.

Twelve females, twelve males, fifty-two juveniles (J1-J3) from Shanxi province and ten females, four males, thirty juveniles (J1-J3) from Beijing.

Description.

Measurements (see Tables 1 and 2).

Female. Body habitus G-shaped when relaxed by gentle heat (Fig. 1M) gradually tapering in both ends. Cuticle under light microscope with three distinct layers, the middle one consisting of several sub-layers, slightly refractive, most pronounced at labial and tail regions, the inner one thicker at labial and tail region with radial striations, cuticle 6 μm thick at post-labial area, 5 μm along the body and 11 μm in post-anal region. Nine lateral, three dorsal and five ventral body pores in the neck region. Lip region slightly expanded, broadly rounded frontally and laterally (Fig. 2D). Amphidial fovea broad and symmetrically bilobed at the base (Fig. 3B). Odontostyle long and slender with simple base, odontophore slightly swollen at the base (Fig. 3A), approx. 1/3 of the odontostyle length. Guide ring located far posterior from oral aperture (Fig. 4 A–B). Pharynx dorylaimoid with anterior part more or less coiled, pharyngeal bulb comparatively short measuring 107-138 × 23-28 μm (Fig. 1O). Arrangement of pharyngeal glands normal, dorsal gland nucleus located at 23-34 μm and ventrosublateral gland nuclei at 48-54 μm from the beginning of pharyngeal bulb. Pharyngo-intestinal valve (cardia) hemispherical (Fig. 1P). Tail short dorsally convex and terminus bluntly conoid with two pairs of caudal pores (Fig. 2I). Vulva a transverse slit located slightly anterior from mid body (V = 40-48 %), vagina well developed extending nearly half of body diameter (Fig. 3D, E). Reproductive system amphidelphic with anterior and posterior branches almost equally developed (Fig. 3C). Sperms observed in the uteri of most females (Fig. 3F).

Male. Morphologically similar to female. Body G to spiral shape (Fig. 1M). Testes paired and fully developed. Sperms abundant and irregularly shaped (Fig. 3K). Spicules robust (Fig. 3J). Lateral guiding piece 32-35 μm. Two ad-cloacal pairs of supplements preceded by row of 10-14 ventromedian supplements (Fig. 3H). Tail ventrally curved bluntly conoid to hemispherical, 2-3 lateral pores on each side (Fig. 3H).

Juveniles. Three juvenile stages (J1-J3) distinctly separated by differences in the body length, odontostyle and replacement odontostyle length (Fig. 1 A–C). In the first stage juvenile, the anterior part of replacement odontostyle is inserted in the wall of odontophore (Fig. 3A). Morphologically, juveniles resemble adults except for the smaller size and not developed reproductive system. Habitus assuming J shape does not change with the stage (Fig. 1 I–K). Tail length does not change while anal width increases (Fig. 1E-G) thus c’ ratio decreases (Table 2), guide ring position becoming more posterior during successive stages (Fig. 2 A–C). First stage juvenile is characterized by a conoid tail becoming bluntly conoid in second to third stages (Fig. 2 F–H).

Sequences and phylogenetic analyses.

The length of PCR products based on gel images of the amplification of partial 18S and D2-D3 region of 28S RNA genes of L. cheni sp. n. (LDT235 and BJ07) was 844 bps and 856 bps, respectively. The sequences of both populations were identical. The phylogenetic relationships of L. cheni sp. n. with the closest species inferred from analyses of the partial 18S rDNA and D2-D3 expansion segments of 28S rDNA sequences using BI are presented in Figs 6 and 7, respectively. In general, the new species grouped with other Longidorus species of predominantly Asiatic origin in both phylogenetic reconstructions. In D2-D3 rDNA phylogenetic tree, L. cheni clustered in a well-supported clade comprising four species from China ( L. juglans (MF318878), L. fangi (MF318883-84), Longidorus sp. (KF280150); one from Japan ( L. jonesi (KF552069) and two species from North America, USA ( L. diadecturus (AY601584) and Longidorus sp. (KF242342-43)). With exception of the species for which there are no descriptions, all mentioned species have a guide ring at mid-odontostyle area. Similarly, in the 18S rDNA phylogenetic reconstruction L. cheni sp. n. clustered with the same group of species ( L. jonesi , L. fangi , and L. diadecturus ) and L. litchii (AY687996) that has no D2-D3 rDNA sequence deposited in GenBank. The percentage dissimilarities of L. cheni to the closest species L. litchii , L. fangi , and L. juglans in 18S rRNA gene were 1.5 %, 1.8 %, and 1.8 %, respectively (a total of 955 positions in the final dataset). Much higher were the pairwise percentage distances of L. cheni sp. n. to the closest species in D2-D3 28S rRNA gene ranging from 16.8-16.9 % ( L. fangi and L. jonesi ) to 18.3 % ( L. juglans ).

Type habitat and locality.

Specimens were recovered from soil around the roots of a conifer ( L. principis-rupprechtii ) and Chinese firethorn ( P. fortuneana ) in mountainous region of Shanxi and botanic garden in Beijing, China, GPS coordinates 37°50'815"N, 111°27'253"E and 30°34'54.7"N, 114°15'40.9"E, respectively.

Type material.

Holotype. Female slide no. LS5313 and paratypes (slides no. LS 5301-5312, LS 5314-5350) includes 12 females, 12 males and 52 juveniles deposited in the Nematode collection C602 Nematology laboratory of Zhejiang University, Hangzhou, China. One female, one male, three juveniles deposited at the nematode collection of the Institute of Biodiversity and Ecosystem Research, Bulgarian Academy of Sciences, Sofia, Bulgaria.

Etymology.

The species is named after Prof. Pinsan Chen, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, one of the pioneer plant nematologists in China.

Diagnosis and relationship.

Longidorus cheni sp. n. is an amphimictic species characterized by females with medium body size (L = 4.1-6.6 mm), assuming G-shape, lip region 16-23 μm wide, posteriorly situated guide ring (at 70-93 μm from anterior end), long odontostyle (142-168 μm), odontophore base slightly swollen, tail short (24-33 μm) and bluntly conoid to rounded. Males abundant, spicules 111-123 μm long, ventromedian supplements 10-14. Three juvenile stages present. The tail of the first stage juvenile conoid, tail shape in the second and third stage juveniles gradually becoming rounded. Finally, the species have specific ribosomal sequences KY284157 and KF270638 for D2-D3 expansion domains of 28S rDNA, KF261570 and MG656980 for the 18S rDNA region. The identification codes of L. cheni sp. n. based on the polytomous key by Chen et al. (1997) and additional codes ( Peneva et al. 2013) are: A6-B3-C5-D12-E2-F3-G1-H1-I2-J2-K2.

Longidorus cheni sp. n. belongs to a group of species ( L. jonesi -group) having guide ring at mid-odontostyle area ( Xu et al. 2017) which consists of L. diadecturus Eveleigh & Allen, 1982, L. fursti Heyns, Coomans, Hutsebaut & Swart, 1987, L. himalayensis (Khan, 1986) Xu & Hooper, 1990, L. ishigakiensis Hirata, 2002, L. jagerae Heyns & Swart, 1998, L. jonesi Siddiqi, 1962, L. juglans , L. laricis Hirata, 1995, L. litchii , L. macromucronatus Siddiqi, 1962, L. martini Merny, 1966, L. naganensis Hirata, 1995, L. orongorongensis Yeates, Van Etteger & Hooper, 1992, and L. waikouaitii Yeates, Boag & Brown, 1997 (See Tables 3 and 4).

Longidorus cheni sp. n. morphologically is most similar to L. naganensis from which it can be distinguished by having different first stage juvenile tail (broadly rounded vs digitate with mucro ( c’ = 1.02-1.46 vsc’ = 2.0-2.5), males abundant vs males absent ( Hirata 1995). Furthermore, it can be differentiated from all other species belonging to this group. It differs from:

L. juglans by females having a longer odontostyle (143-168 vs 107-120 μm), different amphidial fovea shape (bilobed vs non-bilobed) ( Xu et al. 2017);

L. laricis by females having a smaller a ratio (45.7-63.1 vs 83-108), males abundant vs males rare, longer spicules (101-124 vs 66.2 μm), different tail shape in J1 (conoid, c’ = 1.02-1.46 vs elongate conoid with a digitate tip, c’ = 1.8-2.4) ( Hirata 1995);

L. litchii by females having a smaller a ratio (45.7-63.1 vs 72-84), wider lip region (17.5-23 vs 12.5-14 μm), smaller V ratio (40-49.4 vs 49-54), longer spicules (101-124 vs 68.5-71 μm), number of ventromedian supplements (10-14 vs 6-7), number of stages (3 vs 4), different tail shape in J1 (bluntly conoid, c’ = 1.02-1.46 vs elongate conoid with a long digitate tip, c’ = 2.72-3.42) ( Xu and Cheng 1992), odontophore base (slightly vs strongly flanged ( Zheng et al. 2002);

L. fangi by females having a smaller a ratio (45.7-63.1 vs 81-98), amphidial fovea shape (bilobed vs non-bilobed), longer odontostyle (142-168 vs 124-144 μm), lower c’ ratio in J1 ( c’ = 1.02-1.46 vsc’ = 1.58-2.2) ( Xu and Cheng 1991);

L. fursti by females having a smaller a ratio (45.7-63.1 vs 105-137), wider lip region (17.5-23 vs 14.5-16 μm), different amphidial pouch shape (bilobed vs non-bilobed), longer odontostyle (142-168 vs 99.5-108 μm), smaller V ratio (40-49.4 vs 51.5-53.6), lower c’ ratio in J1 ( c’ = 1.02-1.46 vsc’ = 2.84-2.93) ( Heyns et al. 1987);

L. himalayensis by females having a longer (L = 4.1-6.6 mm vs L = 3.42-3.9) and more plump body (a = 45.7-63.1 vsa = 97.8-112), a wider lip region (18-23 vs 14-15 μm), longer odontostyle (142-168 vs 115-125 μm), more posteriorly situated guide ring (70-91 vs 55-60 μm) ( Khan 1986);

L. ishigakiensis by females having a smaller a ratio (45.7-63.1 vs 106-130), wider lip region (18-23 vs 13-14 μm), different amphidial pouch shape (bilobed vs non-bilobed), smaller c’ ratio ( c’ = 0.62-0.86 vsc’ = 1.0-1.2), different tail shape in J1 (bluntly conoid, c’ = 1.02-1.46 vs rounded, c’ = 1.9-2.5), males abundant vs males absent ( Hirata 2002);

L. jagerae by females having a differently shaped lip region (not expanded vs expanded), more plump body (a = 45.7-63.1 vsa = 89-107), longer odontostyle (142-168 vs 95-109 μm), more anteriorly situated vulva (V = 40.0-49.4 vsV = 51.5-56.3), prerectal inclusions (absent vs present) (Heyns and Swart, 1998);

L. jonesi by females having a longer body (L = 4.1-6.6 vs L = 3.17-3.8 mm) and odontostyle (142-168 vs 107-120 μm), more posteriorly situated guide ring (70-91 vs 57-66 μm), more anteriorly situated vulva (V = 40.0-49.4 vsV = 50-52.4) ( Siddiqi 1962);

L. martini by females having a longer body (L = 4.1-6.6 vs L = 3.18-4.29 mm) and odontostyle (142-168 vs 83-96 μm), more posteriorly situated guide ring (70-91 vs 51-66 μm), more anteriorly situated vulva (V = 40.0-49.4 vsV = 52-56) ( Merny 1966);

L. diadecturus by females having a longer body (L = 4.1-6.6 vs L = 3.32-4.02 mm), odontostyle (143-168 vs 109-121 μm) and pharyngeal bulb (107-138 vs 62-83 μm), more posteriorly situated guide ring (70-91 vs 50-64 μm) ( Eveleigh and Allen 1982);

L. orongorongensis by females having a shorter and more plump body (L = 4.1-6.6, a = 45.7-63.1 vs L = 6.0-8 mm, a = 81-106), more posterior guide ring po sition (70-91 vs 63-73 μm), smaller V ratio (40-49.4 vs 49-54), longer spicule (101-104 vs 84-87 μm) ( Yeates et al. 1992);

L. macromucronatus by females having a plumper body (a = 45.7-63.1 vsa = 94-105), a wider lip region (17.5-23 vs 14 μm), longer odontostyle (142-173 vs 117-128 μm), 3 vs 4 juvenile stages, differently shaped tail in J1 (broadly conoid vs sub-digitate c’ = 1.02-1.46 vsc’ = 0.63-0.8) ( Siddiqi 1962);

L. waikouaitii by having differently shaped amphidial fovea (pocket shaped, bilobed at the base vs funnel shaped), a longer odontostyle (142-173 vs 113-117 μm), more posterior position of the guide ring (70-91 vs 56.5-59.5 μm), males abundant vs males absent (Yeates et al. 1997).