Compendium of the Genus Psilenchus de Man, 1921 (Tylenchida: Psilenchidae)

Yawar Iqbal Erum*, Hussain Sagir, Kazi Nasira and Fayyaz Shahina

National Nematological Research Centre, University of Karachi, Karachi-75270, Pakistan.

Received | September 03, 2020; Accepted | November 10, 2020; Published | November 22, 2020

*Correspondence | Yawar Iqbal Erum, National Nematological Research Centre, University of Karachi, Karachi-75270, Pakistan; Email: erum_i@yahoo.com

Citation | Erum, Y.I., Sagir, H., Nasira, K. and Shahina, F., 2020. Compendium of the Genus Psilenchus de Man, 1921 (Tylenchida: Psilenchidae). Pakistan Journal of Nematology, 38(2): 124-129.

DOI | http://dx.doi.org/10.17582/journal.pjn/2020/124.129

Keywords | Compendium, Psilenchus, Re-description, Tylenchida, Morphometric and allometric characters

Introduction

The genus Psilenchus was established by de Man (1921) with P. hilarulus as the type species, a species of nematodes with didelphic ovary, stylet without knobs, head with distinct amphidial aperture, post labial, median bulb posterior to middle of oesophagus, adanal bursa, tail clavate or cylindroid to small rounded terminus in both sexes. Later on, Thorne, 1949 described the genus Psilenchus in more detail and added four new species viz., P. striatus, P. magnidens, P. gracilis and P aberrans and placed Tylenchus clavicaudatus Micoletzky, 1922 under the genus Psilenchus. Later on, two species were transferred to Basiria by Siddiqi, 1963 as B. aberrans (Thorne, 1949; Siddiqi, 1963) and B. gracilis (Thorne, 1949; Siddiqi, 1963). Afterwards Thorne and Malik, 1968 transferred P. magnidens to Neopsilenchus. Luc et al., 1987 and Ryss, 1993 regarded Psilenchus de Man (1921) Atetylenchus Cobb, 1913 and Antarctenchus Spaull, 1972 representing as the most primitive taxa of Tylenchida. Siddiqi, 2000 clearly differentiated the family Psilenchidae Paramonove, 1967 (Khan, 1969) from Tylenchidae Orley, 1880 in having didelphic ovary and the presence of phasmids on the tail, and placed it in the superfamily Dolichodoroidea in (Chitwood, 1950) Siddiqi, 1986 of the suborder Hoplolaimina Chizhov and Berezina, 1988. He divided the family Psilenchidae into two subfamilies, (i) Psilenchinae Paramonove, 1967 (stylet not knobbed, vulva without lateral membrane and epiptygma) with two genera Atetylenchus and Psilenchus; and (ii) Antarctenchinae Spaull, 1972 (stylet knobbed, vulva with lateral membrane and epiptygma) with one genus Antarctenchus. In Psilenchus cephalic region appearing smooth, amphidial aperture distinct, post labial, median bulb posterior to middle of oesophagus whereas Atetylenchus was characterized by cephalic region distinctly annulated, amphidial aperture indistinct, labial, median bulb anterior to middle of oesophagus. Seven species of the genus Psilenchus have so far been reported from Pakistan (Shahina et al., 2019).

 

Materials and Methods

In the compendium fifteen characters (allometric and morphometric) are used to separate Psilenchus species (Table 1). Drawing of anterior and posterior ends of 19 species were taken from original publications or subsequent re-descriptions (Figures 1-3).

 

 

 

Genus Psilenchus de Man, 1921

Diagnosis: Medium sized to large nematodes (0.7-1.70 mm), straight to curve when heat relaxed. Cuticle distinctly annulated, lateral field with four incisures, inner lines often indistinct. Amphidial aperture generally distinct as transverse slits at base of lateral lip areas. Cephalic region continuous or slightly narrower than body. Cephalic framework weekly developed. Stylet cylindrical, cone about one third oftylet length, basal knobs absent but minute swellings may occur. Median bulb prominent with distinct thickenings of lumen wall, usually behind middle of oesophagus. Basal bulb small, pyriform. Cardia discoidal or rounded. Female reproductive system paired, outstretched in opposite directions. Vulva without lateral vulval membranes, spermatheca axial and elongated. Tail elongated or shorter and thicker, with clavate or nonclavate rounded tip. Distinct phasmids on tail, anterior to its middle. Bursa adanal, prominent. Spicules tylenchoid 25-33µm long. Gubernaculum simple, fixed trough shaped. An updated list of valid 19 species of the genus Psilenchus is given below:

Type species: Psilenchus hilarulus de Man, 1921

Other species: P. aestuaris Andrassy, 1962; P. bahiablancae Doucet, 1996; P. bilineatus Mizokubo and Nakasono, 1987; P. clavicaudatus (Micoletzky, 1922), Thorne, 1949; P. curcumerus Rahaman et al., 1994; P. dunensis Thapa and Ganguly, 1999; P. elegans Thorne and Malik, 1968; P. gigas Thorne and Malik, 1968; P. hilarus Siddiqi, 1963; P. iranicus Kheiri, 1970; P. khuzdarensis Khan et al., 2004; P. magnificus Lal and Khan, 1990; P. minor Siddiqi, 1963; P. mixus Bajaj, 1997; P. pratensis Doucet, 1996; P. pini Lal and Khan, 1990; P. striatus Thorne, 1949; P. vinciguerrae Brezeski, 1991.

 

 

Discussing the systematics of the genus, De Ley et al., 2006 in the modified classification of Phylum Nematoda on molecular studies placed the genus under the family Tylenchidae; while Siddiqi, 2000 included the genus Psilenchus in the family Psilenchidae. The adanal bursa and long tail distinguished the familyPsilenchidae from the other families of

 

Table 1: Compendium of the genus Psilenchus de Man, 1921.

 

Hoplolaimina, Dolichodoroidea. This family resembles in the short stylet, structure of oesophagus and long tail with the family Tylenchidae but the paired ovaries and the presence of phasmids clearly distinguished it from Tylenchidae. In the present paper authors agreed with the opinion of Siddiqi, 1986, 2000 that the paired gonad and the presence of caudal phasmids appear to be the essential distinguishing characters of Psilenchidae. At present, 19 species are considered valid of the genus according to Siddiqi, 2000 and Geraert, 2008. From Pakistan seven species of the genus Psilenchus have so far been reported among them one new species P. khuzdarensis was described by Khan et al., 2004 from pomegranate (Punica granatum L.) from district Khuzdar, Balochistan Province. Two species P. aestuarius Andrassy, 1962 and P. iranicus Kheiri, 1970 are reported for the first time from Pakistan by Shahina and Maqbool, 1992 from banana field of Sindh. Erum and Shahina, 2010 reported P. pratensis Doucet, 1996 as a new record species from wheat field of Khyber Pakhtunkhwa Province. Khan and Bilqees 1993 and 1994 reported P. minor from walnut (Juglans spp.) and paddy crops (Oryza sativa L.), respectively from Bajore Agency, Khyber Pakhtunkhwa Province for the first time from Pakistan.

Saeed and Ashrafi, 1973 reported P. hilarus Siddiqi, 1963 from Achras zapota in Malir Karachi. Association of this species with the roots of Achras zapota is a new record. P. hilarulus de Man, 1880 was reported by Saeed and Ghaffar, 1979 in a survey of stylet bearing nematodes collected from soil around the roots of sapodilla. This species occurring in 42% of the samples. Maqbool, 1986 and 1988 reported P. hilarulus and P. hilarus from Carica papaya from KP, Punjab and Sindh. Shahina and Maqbool, 1992 reported P. hilarulus and P. hilarus from banana filed in Sindh. Gul and Saifullah, 1991, during the survey of nematodes reported P. hilarus from wheat field in KP, while Maqbool, 1992; also reported this species from wheat. Maqbool, 1988 reported P. hilarulus from barley (Hordeum vulgare) and wheat (Triticum aestivum). Islam et al., 1994 reported P. hilarulus associated with apple trees in Swat, KP, Pakistan. Maqbool, 1992 reported P. hilarulus from various host viz., Lycopericon esculentum, Nicotiana tabacum, oryza sativa, Prunus armeniaca and Punigranatum. Maqbool et al., 1975 reported P. hilarulus from sugarcane in Sindh. Qasim and Ahmad, 1989 reported P. hilarulus from potato Solanum tuburosum) in the northern areas of Pakistan. The genus Psilenchus was also reported by many early researchers but up to generic level only from different hosts and localities (Maqbool and Shahina, 2001; Zarina and Shahina, 2012).

The aim of this study is to congregate the comprehensive information and consolidate the valuable contributions on plant-parasitic nematode, Psilenchus. It provides the complete review of the Psilenchus species described and reported from Pakistan by various researchers from time to time and also discussed the systematic position of this genus. A complete list of valid Psilenchus species is also incorporated in this compendium along with their morphometrics and illustrations for the convenience of the researchers.

 

Novelty Statement

The aim of this study is to congregate the comprehensive information and consolidate the valuable contributions on plant-parasitic nematode, Psilenchus. It provides the complete review of the Psilenchus species described and reported from Pakistan.

 

Author’s Contribution

Yawar Iqbal Erum, prepared the manuscript. Hussain Sagir, conducted the field survey, collected and processed the soil samples. Kazi Nasira, provided technical assistance in preparing the compendium. Fayyaz Shahina, reviewed the manuscript.

Conflict of interest

The authors have declared no conflict of interest.

 

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