Nematology, 2007, Vol. 9(2), 251-260 A key and diagnostic compendium to the species of the genus Merlinius Siddiqi, 1970 (Nematoda: Tylenchida) with description of Merlinius khuzdarensis n. sp. associated with date palm ∗ Zafar A. HANDOO 1, ,AlyKHAN 2 and Shamsul ISLAM 2 1 Nematology Laboratory, USDA, ARS, BARC-West, Bldg 011A, RM 159, Beltsville, MD 20705, USA 2 Crops Disease Research Institute, Pakistan Agricultural Research Council, University of Karachi, Karachi-75270, Pakistan Received: 17 February 2006; revised: 16 January 2007 Accepted for publication: 18 January 2007 Summary – An identification key to 32 valid species of stunt nematodes (Merlinius spp.) is given. A compendium of the most important diagnostic characters for use in identification of species is included as a practical alternative and supplement to the key. The diagnosis of Merlinius is emended and a list of all valid species of the genus is given. The characters most useful for separating species include body and stylet lengths, shape of head, tail and tail terminus, number of head and tail annules, position of vulva (V), and c ratio in females. Also useful are length and shape of spicules and gubernacula in males. A new stunt nematode, Merlinius khuzdarensis n. sp., from the rhizosphere of date palm (Phoenix dactylifera L.) from Khuzdar, Balochistan Province, Pakistan, is described and illustrated. This new species resembles M. bavaricus, M. communicus, M. bilqeesae and M. montanus, but differs from these species by the following: body and stylet length, shape of head, tail and tail terminus, number of head and tail annules, and position of phasmids. Because this species is limited in distribution, its economic importance in date palm and other cultivated crops within the region is not known. Keywords – Balochistan, identification, Khuzdar, morphology, morphometrics, stunt nematodes, taxonomy. The genus Merlinius was established by Siddiqi (1970) the subfamily Telotylenchinae in the family Belonolaimi- to accommodate those forms previously in Tylenchorhyn- dae. In a review of species of agriculturally important Ty- chus that have six incisures in the lateral field, a small lenchorhynchus, Merlinius and Amplimerlinius, Anderson trough-shaped nonprotrusible gubernaculum, and stout and Potter (1991) also presented a good historical back- spicules with distal ends notched and without large ground of stunt nematode taxonomy. Brzeski (1998) in- ventral flanges. Tarjan (1973) gave a valuable synopsis, cluded all species of Merlinius in Geocenamus and gave a key and diagnostic data of the genera and species of key to only 19 species and a compendium for 77 species. Tylenchorhynchinae, and discussed some of Siddiqi’s However, he concluded that the genus Geocenamus may characters. Tarjan (1973) agreed with Siddiqi (1970) be a collective group that could be split into separate that the six-incisure character is consistent and easily genera, but additional investigations, including scanning recognisable and that establishment of Merlinius made the electron microscope studies of cephalic structure, were unwieldy genus Tylenchorhynchus less cumbersome, and needed for more of the species before any action could Merlinius, therefore, justifiable. The present authors agree be taken. with both Siddiqi (1970) and Tarjan (1973) because their A number of taxonomic changes to stunt nematodes action makes it easier to handle this complex and large were proposed by different workers (Siddiqi, 1979, 1986, group of nematodes. At present Merlinius comprises 32 2000; Baldwin & Bell, 1981; Lewis & Golden, 1981; valid species of worldwide distribution that parasitise a Sturhan, 1981; Anderson & Ebsary, 1982; Jairajpuri, wide variety of plants. 1982; Mulk & Siddiqi, 1982; Powers et al., 1983; Jaira- The history of Merlinius was discussed by Hooper jpuri & Hunt, 1984; Skwiercz, 1984; Fortuner & Luc, (1978). Fortuner and Luc (1987) included Merlinius in 1987; Golden et al., 1987; Maqbool & Shahina, 1987; ∗ Corresponding author, e-mail: [email protected] © Koninklijke Brill NV, Leiden, 2007 251 Also available online - www.brill.nl/nemy Z.A. Handoo et al. Mahajan, 1988; Rey & Mahajan, 1988; Esser, 1991; hydrate before being mounted in glycerin on permanent Brzeski & Dolinski, 1998; Handoo, 2000). As a result of slides for observation and measurements (Hooper, 1986). these changes, compilation and development of a dichoto- Line drawings were made with the help of a drawing tube mous key to species of Merlinius have become increas- attached to the microscope and photomicrographs of spec- ingly difficult. Many of the species included in Merlinius imens were made with a 35 mm camera attached to a com- have been placed in new genera by different workers, and pound microscope where measurements were made with several species within other related genera have been ei- an ocular micrometer. ther shifted or synonymised by several workers. The most important character used in distinguishing these genera is the number of lines, ranging from three to six, in the lat- Genus Merlinius Siddiqi, 1970 eral field. In the present study Merlinius is defined as con- taining only those species with six lines in the lateral field. EMENDED DIAGNOSIS (AFTER SIDDIQI, 2000) The objectives of this study were: i) to describe a Merliniinae. Usually under 1 mm long (except M. adak- new species of Merlinius found in soil around roots of ensis Bernard, 1984, M. graminicola (Kirjanova, 1951) date palm from Balochistan, Pakistan; ii) to examine Siddiqi, 1976 and M. productus (Thorne, 1949) Sher, in detail representative specimens and publish data on 1974), straight to arcuate upon relaxation. Body cuticle Merlinius species; iii) to determine the interrelationships lacking longitudinal striae or grooves; lateral field with of the species and to define the valid and most significant six incisures, normally not areolated posterior to pharyn- differentiating characters; and iv) to prepare a new key and geal region. Deirids distinct, in four-incisure region of lat- compendium containing morphometric and related details eral field. Cephalic region continuous or slightly set off, to facilitate easy identification of 32 valid Merlinius not bulbous; annules broken by six radial grooves; peri- species. oral disc indistinct, hexagonal, not well demarcated from surrounding labial area; submedian sectors wider than lat- Materials and methods eral sectors bearing amphidial apertures located posterior to border of oral plate. Stylet usually under 20 µm long (except M. adakensis where it is 34 (32-36) µm long). Paratype specimens of seven species (M. brevidens Vulva closed, slit-like; epiptygma indistinct. Female tail (Allen, 1955) Siddiqi, 1970, M. acuminatus Minagwa, conoid to subcylindrical, pointed or occasionally with a 1985, M. adakensis Bernard, 1984, M. khuzdarensis n. mucro. Spicules cylindroid, straight to slightly arcuate, tip sp., M. montanus Maqbool & Shahina, 1987; M. proces- blunt to notched. Gubernaculum crescent-shaped in lateral sus Siddiqi, 1979) and non-type specimens of four other view. species were examined from the USDA Nematode Collec- tion at Beltsville, MD, USA. These specimens were either mounted in glycerin or were preserved in 3% formalde- TYPE SPECIES hyde and 2% glycerin solution in vials, which ranged Merlinius brevidens (Allen, 1955) Siddiqi, 1970 in number from one to 25, and were accompanied by = Tylenchorhynchus brevidens Allen, 1955 pertinent records. Examinations were made with a com- = Geocenamus brevidens (Allen, 1955) Brzeski, 1991 pound light microscope usually at highest magnifications, and morphometric data were obtained with an eyepiece ∗ OTHER VALID SPECIES micrometer. In evaluation of the species, our own data and the original descriptions of most species, as well as M. acuminatus Minagawa, 1985 any subsequent re-description or other related data, were M. adakensis Bernard, 1984 utilised for the arrangement of the compendium included M. alboranensis (Tobar Jiménez, 1970) Tarjan, 1973 in Table 1. M. bavaricus (Sturhan, 1966) Siddiqi, 1970 Specimens of the new species of Merlinius were ob- M. bijnorensis Khan, 1971 tained from soil around roots of date palm from Khuzdar, M. bilqeesae Khan & Khan, 1995 Balochistan Province, Pakistan and were extracted from M. bogdanovikatjkovi (Kirjanova, 1941) Siddiqi, 1970 soil by sieving and Baermann funnel extraction, killed M. capitonis Ivanova, 1983 by gentle heat, fixed in TAF, then transferred to solu- tion containing traces of picric acid and allowed to de- ∗ Synonymy as in Siddiqi (2000). 252 Nematology Vol. 9(2), 2007 Table 1. Diagnostic data on species of Merlinius. Species L a b c V Lip Lip Stylet Tail Tail Tail Tail c Spicule Gub (mm) region1 annules (µm) annules shape2 terminus3 tip4 (µm) (µm) acuminatus 0.63 ± 0.39 26.7 ± 1.5 5.6 ± 0.3 12.4 ± 1.1 54.7 ± 1.1 OFF 5-8 13.2 ± 0.4 CON FR, POINT SMO 3.2 ± 0.5 22.8 ± 1.8 7.8 ± 0.7 (0.56-0.72) (23.7-29.5) (4.9-6.4) (10.1-14.4) (52.6-56.7) (12.7-14.0) 42-79 (2.3-4.4) (20.0-26.7) (6.7-9.7) adakensis 1.13 ± 0.94 32.8 ± 2.4 6.2 ± 0.4 12.5 ± 1.0 54 ± 1.5 OFF 6-8 34 ± 1.3 54 SCYL BR SMO 3.6 ± 0.3 33 8 (0.96-1.28) (27-37) (5.5-6.8) (10.6-14.2) (51-58) (32-36) (49-68) (3.1-4.1) (30-35) (7-10) alboranensis 0.45 ± 0.01 26.4 4.9 13.8 59.3 OFF 6 11 26-33 SCYL SHEM SMO 2.4-2.8 18.4 6.3 (0.43-0.47) (24.6-29.6) (4.5-5.3) (12.4-15.1) (57.7-60.5) (16.9-20.4) (5.4-7.3) bavaricus 0.75 28 5.2 13 57 CNT 4 21 49-52 SCYL SHEM SMO 2.9 – – bijnorensis 0.63 29.5 4.4 13.2 55.7 CNT 5 20 32-37 SCYL HEM SMO – 23 9 (8-10) (0.56-0.71) (25-34)