Ditylenchus medicaginis Wasilewska, 1965

Hashemi, Kobra & Karegar, Akbar, 2019, Description of Ditylenchus paraparvus n. sp. from Iran with an updated list of Ditylenchus Filipjev, 1936 (Nematoda: Anguinidae), Zootaxa 4651 (1), pp. 85-113 : 94

6. Ditylenchus medicaginis Wasilewska, 1965

153 females: L = 785 (476–1228) µm; stylet = 7.4 (6.5–8.5) µm; pharynx = 123 (96–183) µm; tail = 76.9 (44–112) µm; a = 42.3 (29.3–58.4); b = 6.4 (4.6–8.9); c = 10.3 (7.8–16.2); c′ = 6.4 (3.7–10.5); V = 79.7 (71.3–84.9); V′ = 88.4 (79.5–91.7); PUS/VBW = 1.5 (0.8–3.3); PUS/V-A = 32.4 (15.3–59.2) %; V-A/T = 1.1 (0.7–1.9).

44 males: L = 708 (501–954) µm; stylet = 7.4 (7–8.5) µm; pharynx = 120 (93–166) µm; tail = 75.4 (47–104) µm; a = 44.4 (28.8–62.9); b = 5.9 (4.5–8.5); c = 9.6 (7.3–13.1); c′ = 6.0 (4.3–8.5); spicules = 17.6 (15–22) µm.

Diagnosis. D. medicaginis is distinguished by six lateral field incisures, delicate, short stylet with rounded knobs, pyriform basal pharyngeal bulb (in one specimen elongate), usually offset and sometimes with a slight overlap (up to about 9 µm), variable position of vulva and length of post-vulval uterine sac, rather thin tail with usually pointed to dull and sometimes rounded or seldom mucronate, terminus, and spicule length.

The Iranian populations of D. medicaginis are close to 11 species, including D. acutatus Brzeski, 1991 , D. anchilisposomus , D. apus , D. dauniae , D. elegans Zell, 1988 , D. geraerti , D. myceliophagus , D. silvaticus , D. tenuidens , D. triformis and D. valveus . D. medicaginis differs from D. acutatus by a lower PUS/VBW ratio (1.5 (0.8–3.3) vs. 3.5 (2.8–4.1)), different tail shape (narrow with pointed to rounded tip vs. thick with pointed tip) and lower V-A/T ratio (0.7–1.9 vs. 2.0–2.5), from D. anchilisposomus by its usually pyriform, offset basal pharyngeal bulb (vs. developed basal pharyngeal bulb with long lobe overlapping intestine) and different shape of tail tip (usually pointed vs. usually rounded), from D. apus by greater PUS/VBW ratio (0.8–3.3 vs. 0.2–0.4) and different shape of basal pharyngeal bulb (pyriform and offset vs. elongate and with long overlap), from D. dauniae by having annulated head (vs. smooth), relatively lower V and c′ indices (71.3–84.9 and 3.7–10.5 vs. 83–85 and 3.2–4.1, respectively) and different tail shape (long and narrow vs. short and thick). It can be distinguished from D. elegans by relatively shorter body and tail lengths (476– 1228 and 44 –112 vs. 1030–1370 and 111–149 μm, respectively), from D. geraerti by different tail shape (narrow and relatively long vs. short and thick), from D. myceliophagus by having different development of the cephalic skeleton (medium vs. crescentic and refractive) and by tail shape (narrow with pointed to rounded tip vs. usually thick with rounded tip), from D. silvaticus by different tail shape (narrow, often with pointed to rounded tip vs. thick with pointed or rounded with mucron), from D. tenuidens by annulated head (vs. smooth), and from D. triformis by longer spicules (15–22 vs. 13–15 μm) and six lateral field incisures (vs. four) in anus region.

The closest species to D. medicaginis is D. valveus . Brzeski (1991) stated that the main differences between these species are in the tail shape and relatively posterior vulva position in D. valveus . The general tail shapes in the drawings of Brzeski (1991) do not differ. In addition, the tail tip of D. medicaginis is often pointed or dull, sometimes rounded, and rarely mucronate, while that of D. valveus is usually rounded to dull, and only rarely pointed. In most populations of D. medicaginis in the present study, we observed that the shape of tail tip is diverse even within a population. On the other hand, the V index of both species overlap (72–84 in D. medicaginis and 75–82 in D. valveus ) ( Brzeski 1998). In the description and drawings presented by Brzeski (1998), the S-E pore is in the region of the posterior half of isthmus to the junction of isthmus and basal pharyngeal bulb in D. medicaginis , and near the junction of isthmus and basal pharyngeal bulb in D. valveus . Brzeski (1991, 1998) described D. medicaginis with offset basal pharyngeal bulb and D. valveus with either an offset basal pharyngeal bulb or partial overlap (up to 4 µm). In the present study we observed that in many populations of different Ditylenchus species, a partial overlap of the basal pharyngeal bulb occurs in species with a usually offset basal pharyngeal bulb (such as D. ferepolitor , D. parvus and D. equalis ). Therefore, this character cannot separate these two species. Also we observed that the position of S-E pore is variable even in a single population. Therefore, it seems that D. medicaginis and D. valveus , cannot be reliably separated from each other based solely on morphological and morphometric characters and require further study.