Geocenamus persici, Zhang & Munawar & Castillo & Han & Zheng, 2022

Zhang, Chenying, Munawar, Maria, Castillo, Pablo, Han, Shaojie & Zheng, Jingwu, 2022, Morphological and molecular characterization of Geocenamus persici n. sp. (Nematoda: Merliniinae) from China, Zootaxa 5100 (4), pp. 585-599 : 587-594

Description of Geocenamus persici n. sp.

( Fig. 1−4 )

Measurement. See Table 1 .

Female. Body ventrally arcuate or C-shape after heat relaxation. Lateral field with six incisures, outer bands sometimes irregularly areolated. Under SEM, Body annuli are clearly defined and divided into blocks. Labial region dome-shaped, slightly offset with the body contour and bearing five annuli. The en face view showed a nearly hexagonal labial disc surrounded by the dorsal, ventral sectors, and amphidial apertures. Cephalic framework weak, not refractive. Stylet well-developed and robust with rounded knobs. Dorsal pharyngeal gland orifice located close to stylet base ca 1.9–2.0 µm. Deirids lacking. Median bulb ovate with bean-shaped valve plates. Isthmus slender encircled with nerve ring. Pharyngeal basal bulb saccate, abutting intestine. Excretory pore located in the anterior region of basal pharyngeal bulb. Hemizonid 2–3 annuli long and 0–3 annuli anterior to excretory pore. Reproductive system didelphic with the ovaries outstretched having single row of oocytes. Vulva lips simple, not protuberant; epiptygma minute, double, sunken in vulval cavity under light microscope, clearly visible under SEM observation; vaginal wall thickened at anterior end. Spermatheca bilobed, spherical, offset, filled with rounded sperm cells. Tail long, cylindrical, gradually tapers to rounded, striated terminus. Anus slit like, indistinct, phasmids located in anterior one-third region of tail, ca 12% to 38% posterior to anus.

Male. Common and are similar to females except for the sexual dimorphism. Gonad located on the right side of the intestine and outstretched. Body length and width observed to be shorter than the females. Reproductive system composed of anteriorly outstretched single testis. Spicule curved, 24–30 μm long. Gubernaculum saucer shaped. Bursa encircle the entire tail. Phasmid located 20 to 40% posterior to cloaca.

Type host and locality. The type specimens were extracted from the rhizosphere of the peach tree ( Prunus persica L.), Huzhou, Zhejiang Province, China, on April 25 th, 2021. The geographical position of the sampling site is 11955'51" E; 3048'46" N .

Etymology. The species was found in association with the peach tree ( Prunus persica ), hence the specific epithet is derived from the scientific name of the host.

Type-material. Holotype female, 15 females, and 15 male paratypes (slide number ZJU-33-01-ZJU-33-08) were deposited in the nematode collection of Zhejiang University , Hangzhou, China. Five female and five male paratypes (slide number HZ-01-HZ-04) were deposited at the USDA nematode collection, Beltsville, Maryland, USA. The new species binomial has been registered in the ZooBank database (zoobank.org) under the identifier: urn:lsid:zoobank.org:act:653A67A4-92E5-4CA8-BCC0-9AC5D4DFC6C3 .

Diagnosis and relationships. Geocenamus persici n. sp. can be characterized by females having annulated cuticle with 30−36 longitudinal striae. The lip region dome-shaped and slightly offset from the rest of the body contour. The stylet is slender, 19–22 μm long with rounded knobs; the excretory pore is located at the anterior region of the basal pharyngeal bulb; the vulva is a transverse slit, epiptygma present; the tail is finely annulated and cylindrical having a rounded terminus; male is similar in appearance to that of female; spicule curved 24–31 μm long, gubernaculum is saucer-shaped; bursa encircles the entire tail.

Based on the similar morphology of longitudinal striae and stylet length, Geocenamus persici n. sp. is compared with G. brevicaudatus , G. chengi , G. conicaudatus Ghaderi & Karegar, 2016 , G. quadrifer ( Andrássy, 1954) Brzeski, 1991 , G. rugosus ( Siddiqi, 1963) Brzeski, 1991 , and G. tartuensis ( Krall, 1959) Brzeski, 1991 .

From G. brevicaudatus , it can be differentiated by the shape of lip region (dome-shaped vs hemispherical), fewer lip annuli (5 vs 5–6), shorter stylet of female (20 (19–21) vs 22–25 μm), longer female tail (65 (54–78) vs 25–43 μm), more tail annuli (30–45 vs 14–20), higher c’ value (3.6 (3.1–4.7) vs 1.3–2.1), and the position of phasmids (anterior vs middle of tail).

From G. chengi , it can be differentiated by fewer lip annuli (5 vs 5–6), shorter stylet of female (20 (19–21) vs 20–23 μm), the shape of female tail (cylindrical with broadly rounded terminus vs conical, ending as bluntly pointed terminus), and shorter tail length (65 (54–78) vs 76–92 μm), shorter hyaline terminal region of the female tail (4–5.5 vs 16–21 μm), lower c’ value (3.6 (3.1–4.7) vs 4.6 (4.2–5.5)) and longer spicule (24–32 vs 22–25 μm).

From G. conicaudatus , it can be differentiated by the shape of lip region (dome-shaped vs hemispherical), fewer lip annuli (5 vs 5–6), longer stylet of female (20 (19–21) vs 16.5–19.8 μm), the shape of female tail (cylindrical with broadly rounded terminus vs conical), longer female tail (65 (54–78) vs 39–65 μm), more tail annuli (30–45 vs 20–30), higher c’ value (3.6 (3.1–4.7) vs 2.6–3.3) and tail annulated (vs non-annulated).

From G. quadrifer , it can be differentiated by the shape of lip region (dome-shaped vs variable), deirids absent (vs present), shorter pharynx length (130 (115–151) vs 126–183 μm), longer female tail (65 (54–78) vs 32–49 μm), more tail annuli (30–45 vs 17–27), higher c’ value (3.6 (3.1–4.7) vs 1.6–2.7), tail annulated (vs non-annulated), and the position of phasmids (anterior vs middle of tail).

From G. rugosus , it can be differentiated by longer female body (940 (807–1103) vs 640–930 μm), the shape of lip region (dome-shaped vs variable), fewer lip annuli (5 vs 5–8), shorter stylet of the female (20 (19–21) vs 20–25 μm), shorter pharynx length (130 (115–151) vs 151–178 μm), longer female tail (65 (54–78) vs 43–60 μm), more tail annuli (30–45 vs 19–37), higher c’ value (3.1–4.7 vs 2.2–4.0), and tail annulated (vs non-annulated).

From G. tartuensis , it can be differentiated by the labial framework (non-refractive vs refractive), fewer lip annuli (5 vs 5–6), female stylet (20 (19–21) vs 18–24 μm), shorter pharynx length (130 (115–151) vs 138–182 μm), more tail annuli (35–45 vs 22–33), higher c’ value (3.0–4.7 vs 2.1–3.5), tail annulated (vs non-annulated), and abundant males (vs male rare).

Molecular characterization and phylogenetic relationship. Geocenamus persici n. sp. was molecularly characterized using partial 18S rRNA, D2-D3 region of 28S rRNA, and ITS sequences. The newly obtained sequences were deposited in GenBank with the accessions numbers OL481778 – OL481779 for 18S, OL48174– OL481777 for 28S, and OL481780 – OL481785 for ITS. All the 18S and 28S sequences of the Geocenamus persici n. sp. are identical respectively, whereas the ITS sequences showed slight intraspecific variation, i.e. 99 % similarity (0–1 bp difference).

The 18S tree ( Fig. 5 ) was constructed from 46 Merliniinae taxa with Tylenchorhynchus zeae Sethi & Swarup, 1968 ( KJ461619 ) and Tylenchorhynchus microphasmis Loof, 1960 ( AY593903 ) as outgroup species. Geocenamus persici n. sp. clustered with G. chengi ( MN983268 – MN983270 ) and G. quadrifer ( AY993977 , AY284599 ), whereas the other members of subfamily Merliniinae arranged in separate clades with relatively independent interspecific relationships. The alignment of D2-D3 region of 28S rDNA sequences contained 51 sequences including the sequences from outgroup taxa Coslenchus costatus (de Man) Siddiqi, 1978 , Tylenchorhynchus ventrosignatus Tobar-Jimnez, 1969 ( MT089940 ) and Tylenchorhynchus mediterraneus Handoo, Palomares-Rius , Cantalapiedra-Navarrete, Liebanas, Subbotin & Castillo, 2014 ( KU517198 ) ( Fig. 6 ). In this tree, the new species grouped with G. chengi ( MN983258 − MN983260 ) and G. vietnamensis Nguyen, Linh-Le, Nguyen, Liebanas, Duong-Nguyen & Trinh, 2019 ( MH191361 ) forming a well-supported molecular clade. In the ITS tree ( Fig. 7 ), this new species clade occupies basal position and exhibits a sister relationship with G. chengi ( MN983263 – MN983264 , MN983267 ) and G. vietnamensis ( MH191362 ).

In all the trees, Geocenamus persici n. sp. appeared as a unique species and showed a sister relationship with G. chengi but with significant morphological differences. The sequence identities of the new species with G. chengi are 98% (34 nucleotides, 16 indels differences) for 18S, 98% (12 nucleotides, 2 indels differences) for 28S, and 95% for ITS (32 nucleotides, 5 indels differences).

Figures

FIGURE 1. Line drawings of Geocenamus persici n. sp. A: pharyngeal region; B–D: en face view; E: female lip region; F: lateral lines; G: vaginal area; H: vulval region with posterior reproductive branch; I–K: female tails; L, M: male tails. (Scale bars: A, E–K, M= 10μm; L= 20μm; B–D= 3μm).

FIGURE 2. Light photomicrographs of female Geocenamus persici n. sp. A: Entire body; B–D: anterior pharyngeal region, arrows showing dorsal pharyngeal gland orifice (dgo), and excretory pore (exp); E: posterior pharyngeal region; F–H: vulval regions; I: gonad; J-M: tails regions arrows showing position of anus (a) and phasmid (ph). (Scale bars: A = 100 μm; B = 20 μm; I = 50 μm; C–H & I–M = 10 μm).

FIGURE 3. Light photomicrographs of Male Geocenamus persici n. sp. A: entire body; B: Anterior pharyngeal region arrow pointing towards dorsal pharyngeal gland orifice (dgo); C: posterior pharyngeal region, arrow pointing towards the position of an excretory point (exp); D–H tail with bursa. (Scale bars: A = 100 μm; B = 20 μm; B, C & E–H = 10 μm).

FIGURE 4. Scanning electron micrographs of Geocenamus persici n. sp. A–B: lip region; C: En face view, arrows pointing towards the labial disc (ld) and amphids (am); D, E: vulval region; G, H: female tail regions arrows pointing anus (a); I: lateral field; F, J: cloacal area; K, L: male tail arrow pointing towards phasmid (ph). (Scale bars: A = 5 μm; B = 4 μm; C = 3 μm; D–G & I–J = 10 μm; H, L = 15 μm; K = 20 μm).

FIGURE 5. Phylogenetic relationships of Geocenamus persici n. sp. with other merlinids taxa as inferred from Bayesian analysis using the 18S rRNA gene sequence data set with the GTR+F+I+G4 model. Posterior probability more than 70% is given for appropriate clades. Newly obtained sequences are indicated in bold.

FIGURE 6. Phylogenetic relationships of Geocenamus persici n. sp. with other merlinids taxa as inferred from Bayesian analysis using the D2-D3 of 28S rRNA gene sequence data set with the GTR+F+G4 model. Posterior probability more than 70% is given for appropriate clades. Newly obtained sequences are indicated in bold.

FIGURE 7. Phylogenetic relationships of Geocenamus persici n. sp. with other merlinids taxa as inferred from Bayesian analysis using the ITS rRNA gene sequence data set with the GTR+F+G4 model. Posterior probability more than 70% is given for appropriate clades. Newly obtained sequences are indicated in bold.