Three species of Xiphinema americanum-group complex (Nematoda: Longidoridae), from Lorestan province, Iran

The tribe Longidorini which is a subfamily of Longidorinae (Longidorus spp. and Paralongidorus spp.) accompanied with subfamily Xiphineminae (Xiphinema spp.) are two major plant parasitic nematode groups. Dagger nematodes of the longidorids comprise of plant-parasitic species that cause damage to a vast range of wild and cultivated plants either directly through feeding on plant root cells or indirectly via vectoring of nepoviruses to a wide range of fruit and vegetable crops (Taylor & Brown, 1997; Gutierrez-Gutierrez et al., 2016). The genus Xiphinema has been divided to the X. americanum and X. non-americanum groups.

X. americanum morpho-groups can be characterized by a spiral or C-shaped, small body (1 – 3 mm). Odontostyle 60 – 20 μm. Female reproductive system with two equally developed genital branches, short uteri without uterine differentiation. Presence of symbiotic bacteria in intestinal cells of some juveniles and occasionally in the ovaries of adults. Tail short conical to broadly convex-conoid (Lamberti et al., 2000; Orlando et al., 2016).

The Xiphinema americanum-group consisted of a complex of about 55 species of plant-ectoparasitic nematodes of plants. This group of plant-parasitic nematodes is one of the most difficult Xiphinema species complexes to be diagnosed, because their morphology is very conservative and their morphometric characters are often overlaped (Archidona-Yuste et al., 2016). Ten species of Xiphinema have been reported from Iran. They are X. americanum, X. bacaniboia, X. brevicollum, X. himalayense, X. oxycaudatum, X. pachtaicum, X. pacficum and X. rivesi (Ghaderi et al., 2018), X. simile (Naghavi et al., 2018) and X. primum (Mobasseri, et al., 2020). In the present nematological survey on longidorids in Khorramabad county, Lorestan province, southwest of Iran, three nematode species of the genus Xiphinema namely

X. oxycaudatum, X. pachtaicum and X. plesiopachtaicum were collected from several natural environments and were identified based on morphological and morphometrics characters and out of this three nematode species, X. plesiopachtaicum is a new record for nematode fauna of Iran.

The present survey carried out in forests of Khorramabad district, Lorestan province, south west of Iran, during spring 2018 till late autumn 2019. Khorramabad is located in the middle parts of Zagros Mountain ranges of Iran, due to receiving more than 500 mm precipitation on average annually, it enjoys a rich diversity of plant coverage, including Oaks and hawthorns forest trees. GPS coordinates of the sampling location were: 33°29′ 15′′ E 48º 21′ 15′′. After removing the upper 5 cm of topsoil, 80 Soil samples were randomly collected from 20 to 50 cm depth of the rhizosphere of Brant’s oak (Quercus brantii Lindi.) and hawthorn (Crataegus aronia L.) forest trees. Keeping 50 cm distance from the trees, four soil samples collected from 4 main geographic directions around the tree stems. The soil samples were thoroughly mixed on clean plastic sheet, and about 1 kg of the mixed soil samples were poured in plastic bag as a composite sample. The bag labeled for location, date and tree species of sample collection. Then the bags transferred to the nematology laboratory of Plant protection Department of Lorestan University and they were stored at 4 °C until their processing. Nematodes extraction carried out from 500 cm3 of soil samples using the Brown &Boag (1988) modified method. Additional soil samples were collected if needed afterwards, from the same locations to obtain sufficient specimens for morphological characterization. Specimens for light microscopy were killed using gentle heat, then fixed and processed to pure glycerin adopting the De Grisse (1969) method. Morphological and morphometric criteria of specimens were studied using an Olympus BX31 light microscope equipped with a Dino-eye microscope eye-piece camera in conjunction with Dino Capture version 2.0 software. Raw photographs were edited using Picasa 3.9.138.150. Drawings were made using Corel DRAW^®, software version 12.

The conducted research is neither related to human nor animals use.

Xiphinema plesiopachtaicum Archidona-Yuste, Navas-Cortes, Cantalapiedra-Navarrete, Palomares-Rius and Castillo, 2016

(Figs. 1, 3)

Fig. 1

Fig. 2

Fig. 3

Measurements

See Table 1.

Body medium-sized 1.7 – 1.8 mm, ventrally arcuate upon fixation, tapering toward both ends, habitus usually open C shaped after fixation. Labial region 3.6 – 3.8 μm high, expanded, frontally flattened, laterally rounded, separated from the rest of the body by constriction. Amphid stirrup-shaped 5.5 – 6 μm wide and 63 – 66 % of the corresponding lip region diameter. Odontostyle 8, 8.4 times lip region diameter, odontophore 0.5 times odontostyle with weak flanges 6 – 7.5 μm wide diameter. Pharynx dorylaimoid with basal bulb occupying ca 23 – 25 % of the total length, muscular bulb measuring 11.4 – 12.3×74 – 81 μm. The female reproductive system didelphic-amphidelphic, reflexed, both branches apparently equally developed, anterior and posterior genital branch 225 – 285 μm and 230 – 280 μm long, respectively, ovaries filled with symbiontic bacteria, vulva equatorial, transverse, slit-like, vagina with short distal part and very well developed proximal Part, 57 – 60 % of corresponding body diam. Prerectum 415 – 490 μm long. Rectum 18.5 – 20 μm long. Tail short, dorsoventral depression at hyaline region level, two pairs of caudal pores are present on each side.

Male: Not found.

Faculty of Agriculture and Natural Resources, Khorramabad County, Lorestan province, Iran, (GPS coordinates: N 33° 26′ 17′′ E 48° 15′ 41′′, altitude 1769 m a.s.l.), in the root zone soil of oak (Quercus brantii Lindi.).

X. plesiopachtaicum, is reported for the second time since its original description and for the first time outside Spain. The species X. plesiopachtaicum described by Archidona-Yuste et al., 2016 from the rhizosphere of olive trees in southern Spain for the first time. The present population fits well with the type specimens in most morphological and morphometric characteristics , only slight differences were observed viz shorter odontostyle (73 – 76 vs 77 – 89 μm) and longer tail (27.5 – 30 vs 23.5 – 28.5 μm). Based on the morphological similarities, X. plesiopachtaicum is closely related to X. Pachtaicum (Tulaganov, 1938) Kirjanova, 1951, X. madeirense Brown, Faria, Lamberti, Halbrendt, Agostinelli and Jones, 1988, X. parapachydermum Gutierrz-Guterrez, Cantalapiedra-Navarrete, Decramer, Vovlas, Prior, Palomarres & Castillo, 2012 and X. peruvianum Lamberti and Bleve-Zacheo, 1979. X. plesiopachtaicum could be separated from X. pachtaicum in having a smaller a (61.2 – 66.7 vs 64 – 74) and c´ (1.4 – 1.6 vs 1.7 – 2) ratio and shorter odontostyle (73 – 76 vs 77.6 – 81.6 μm). It can also be differentiated from X. madeirense via a shorter body length (1.7 – 1.8 vs 2 – 2.4 mm), anteriorly located guiding ring (64.5 – 68 vs 82 – 98 μm), shorter odontostyle (73 – 76 vs 100 – 109 μm) and shorter tail (27.5 – 30.6 vs 33 – 44 μm). It differs from X. parapachydermum by smaller c´ value (1.4 – 1.6 vs 1.5 – 2.3), shorter odontostyle (73 – 76 vs 70 – 87.5 μm) and odontophore (42 – 43.7 vs 36.5 – 54.5 μm). Finally, X. plesiopachtaicum can be differentiated from X. peruvianum by greater a value (61.2 – 66.7 vs 45 – 56), shorter odontostyle (73 – 76 vs 85 – 92 μm) and odontophore (42 – 43.5 vs 46 – 52 μm), narrower lip region (8.5 – 9.2 vs 9 – 10.5 μm) and anteriorly located guiding ring (64.5 – 68 vs 67 – 78 μm).

Xiphinema oxycaudatum Lamberti & Bleve-Zacheo, 1979

(Figs. 2, 3)

Measrements

See Table 1.

Body medium-sized 1.5, 1.7 mm, tapering gradually toward the extremities. Labial region rounded separated by a constriction from the rest of the body. Amphidial pouches stirrup-shaped, with slit-like aperture, 4.2, 4.5 μm wide, 39, 40 % of the corresponding lip region diameter. Odontostylet, odontophore and guiding apparatus typical for X. americanum-group, odontostyle robust,7, 7.5 times lip region diameter, odontophore 0.5 times odontostyle with weak flanges, 8.6, 9 μm wide diameter. The oesophageal basal bulb occupies ca 24, 26 % of the oesophagus total length, muscular bulb measuring 15.6, 18.8 × 68.7, 70 μm. The female reproductive system didelphic-amphidelphic with equally developed genital branches, anterior and posterior gonad 200, 264 μm and 239, 255 μm long, respectively, reflexed ovary filled with symbiotic bacteria, vulva transverse, equatorial, vagina occupying 47, 48 % of corresponding body diam. Tail, conoid, dorsally convex, ventrally straight to slightly arcuate with pointed terminus, bearing two caudal pores on each side.

Male: Not found

Faculty of Agriculture and Natural Resources, Khorramabad County, Lorestan province, Iran, (GPS coordinates: N 33° 26′ 17′′ E 48° 15′ 41′′, altitude 1769 m a.s.l.), in the root zone soil of oak (Quercus brantii Lindi.).

This species was previously recorded from rhizosphere of oil palm in Nigeria (Lamberti & Bleve-Zacheo, 1979; Bos & Loof, 1984) and from soil under old mango and baoba tree in Kenya (Coomans & Hens, 1997). In Iran, this species was first observed by Fadaei et al. (2003) from rhizosphere of citrus trees in Hormozgan. The present Iranian females conformed well in most morphological and morphometric characteristics to X. oxycaudatum described by Lamberti & Bleve-Zacheo (1979) except in having wider lip region (10.5 – 11.5 vs 9 – 10 μm). The main features of the specimens, also fit perfectly to those populations described by Fadaei et al. (2003) except in having slightly greater c ratio (50 – 54 vs 37 – 51.5) and moderately greater c´ value (1.3 – 1.4 vs 1.5 – 1.8).

Xiphinema pachtaicum (Tulaganov, 1938) Kirjanova, 1951

(Figs. 3)

Measrements

See Table 1.

Robat Namaki village, Robat area, Khorramabad County, Lorestan province, Iran, (GPS coordinates: N 33° 36′ 31′′ E 48° 18′ 16′′, altitude 1332 m a.s.l.), in the root zone soil of Hawthorn (Crataegus aronia L.).

Xiphinema pachtaicum is a well-known species of worldwide distribution and is probably the most cosmopolitan representative of the X. americanum- group. This species is widely distributed throughout the Mediterranean Basin and in Central Asia. It has also been collected from California and Switzerland, England, and South Africa (Lamberti & Bleve-Zaheo., 1979). Furthermore it is widespread in several countries of Central and Eastern Europe, such as Bulgaria, Croatia, the Czech Republic, Macedonia, Montenegro and Serbia, Moldavia and Ukraine and Slovakia (Repaci et al., 2008). In Iran, X. pachtaicum was first reported from vineyards in East Azarbaijan, West Azarbaijan, Tehran, Esfahan, Lorestan, Khorasan, Sistan and Baluchestan by Mojtahedi et al. (1980), later this species was collected from Ardabil, Kerman, Markazi, Alborz, Kurdistan, Gilan, Zanjan and Hormozgan of Iran from the root zone soil of Beet, Fruit trees, Olive, Potatoe, Tomatoe, Alfalfa, Pistachio, Apricot, Pine, Bean, Walnut and Forest trees (Ghaderi et al., 2018). The Khorramabad population entirely matches with the earlier described populations by Lazarova et al., 2016.