Rev 12/18/2023
Tylenchida Tylenchina Tyl;enchuloidea Tylenchulidae Paratylenchinae
Paratylenchus Micoletzky, 1922
Type species of the genus: Paratylenchus bukowinensis Micoletzky, 1922 Synonyms: Paratylenchoides Raski, 1973
The genus Paratylenchus Raski, 1962 was distinguished from Gracilacus by the following characters:
(Raski, 1976)
Raski (1962) established the genus Gracilacus Raski, 1962, for Paratylenchus species with stylets longer than 48 μm. Raski (1976) reduced the minimum stylet length of the genus Gracilacus to 41 μm. Some nematologists accepted Gracilacus as a valid genus that can be differentiated from Paratylenchus mainly by the different stylet length . Others did not accept the validity of Gracilacus and synonymized it with Paratylenchus . Interestingly, Van den Berg et al. (2014) did not reject Gracilacus based on their molecular analysis and included it in their ITS phylogenetic tree in which the only two species possessing stylets longer than 40 μm (P. aculentus and P. bilineatus) formed a monophyletic group (Zhou et al, 2018)..Recent studies on the ITS rRNA gene showed that phylogenetic relationships of putative species included in Gracilacus are not resolved, and the validity of the genus Gracilacus is in question (Esmaeli et al., 2016). Phani et al (2019) remarked that except for the length of stylet, there appear to be no other significant morphological differences between Gracilacus and Paratylenchus. Consequently, (they preferred to treat Gracilacus as a synonym of Paratylenchus.
Taxonomic Note: The genus Paratylenchus was originally described with P. bukowinensis as the type species (Micoletzky, 1922). There were more than 130 described species of Paratylenchus by 2020. Their identification has become increasingly difficult, mainly due to their similar morphology and the mall differences among many species (Esmaeili et al., 2016; Hosseinvand et al., 2020).
Some species are known to be pathogenic to crops, including P. projectus P. bukowinensis; P. neoamblycephalus P. dianthus and P. hamatus so unambiguous and accurate identification of is necessary for designing effective management strategies and or distinguishing pathogenic from non-pathogenic species (Esmaeili et al., 2016)..
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These nematodes in the family Tylenchulidae are among the smallest plant-parasites, 0.18-0.6 mm long. Cuticular annulation is smooth.
Females: Usually less than 0.5 mm long, vermiform, not swollen, except that gravid female may swell anterior to the vulva.
Labial framework weakly sclerotized (except in P. israelensis and P. sheri where it is stronger)
There is a strong stylet (from 12 to 40 �m , usually about 36 �m ) which allows the nematode to feed several cell layers below the root surface.
Excretory pore between level of nerve ring and level of esophago-intestinal junction.
Females have a single outstretched ovary and the vulva is in the posterior region of the body.
They probably do not feed. However, they may be common in the population.
Juveniles: Juvenile stages resemble the female, but with a smaller stylet.
The stylet is usually absent in the J4 stage. The J4 is a dauer (survival) stage, and development will not proceed beyond this stage unless a host plant is present.
In a 1987 review, Raski and Luc (1987) recognized 64 species.
Size of a Paratylenchus female in relation to some other soil nematodes.
Photos by Howard Ferris
Paratylenchus procorpus and metacorpus
Ghaderi et al. (2014) Provided a key for 177 species considered valid at that time.
Common in native and cultivated soils, especially around roots of woody plants and shrubs.
Paratylenchus is the most commonly occurring genus plant-parasitic of nematodes found in California prune orchards (found in 65 of 97 orchards sampled - Lownsbery data).
D-rated pest in California Nematode Pest Rating System.
Some species are known to be pathogenic to crops, including P. projectus P. bukowinensis; P. neoamblycephalus P. dianthus and P. hamatus For this reason, unambiguous and accurate identification of these nematodes is a prerequisite for designing effective management strategies and for distinguishing pathogenic from non-pathogenic species (Esmaeili et al., 2016)..
Nematode is ectoparasitic but can be somewhat sedentary for periods of time.
Feeds on mature parts of root(?) on epidermal and outer cortical cells; also at wounded areas and lateral root emergence sites.
Wide host range; nematode has been demonstrated to cause damage to celery in New England states and in Holland.
Damage to greenhouse-grown carnations has also been reported.
Life cycle is 30 to 31 days at 25 to 28 C.
J4 is the persistent stage - at least in some species molt of the J4 is stimulated by root diffusates (host presence) - tolerant of cold and desiccation. The J4 do not molt to adults in water, but molt progressively over a 2 week period in root diffusates. In some cases, the root exudates from a host plant did not induce molting of a Paratylenchus species to which it was a host, for example, red clover (Trifolium pratense) is a host for both P. projectus and P. dianthus but only induced molting in P. projectus (Rhoades and Linford, 1959).
In older pot cultures or field soils, the resistant J4 may be 80% of the population.
J4 distinguished from other stages by reduced or absent stylet and esophagus and accumulation of opaque granules in esophagus region (Rhoades and Linford, 1959).
J4 male has no stylet and does not feed, considered an inactive survival stage in adverse conditions.
Female grows after final molt, and may not feed as J4. Gravid females may become quite swollen; the fattening is restricted to that part of the body anterior to the vulva, so that the body posterior to the anus remains slender.
Pin nematodes are found in high numbers on many plants but appear to cause significant damage to only a few. Effects range from no symptoms to shallow localized lesions (Raski and Radewald, 1958). Root tip elongation and lateral root development may be reduced or terminated by the prolonged feeding of many individuals (Ingham & Merrifield, 1996).
Esmaeili, M., Ramin Heydari, Pablo Castillo, Mozhgan Ziaie Bidhendiand Juan E. Palomares-Rius. 2015. Molecular characterisation of two known species of ParatylenchusMicoletzky, 1922 from Iran with notes on the validity of Paratylenchus audriellus Brown, 1959. Nematology 18:591-624. .
Ghaderi, R., Kashi, L., Karegar, A. 2014. Contribution to the study of the genus Paratylenchus Micoletzky, 1922 sensu lato (Nematoda: Tylenchulidae). Zootaxa 3841(2):151–187.
Raski, D.J. and Luc, M. 1987. A reappraisal of Tylenchina (Nematoda) 10. The superfamily Criconematoidea Taylor, 1936. Revue de Nematologie 10:409-444.
Hosseinvand. M., A. Eskandari and R. Ghaderi, 2020. Morphological and molecular characterisation of three known species of Criconematoidea from Iran. Nematology 22:745-758.
Ingham, R., Merrifield, K. 1996. A Guide to Nematode Biology and Management in Mint. Integrated Plant Protection Center, Oregon State University, Corvallis. Pub. No. 996. 38 p.
Micoletzky, H. (1922). Die freilebenden Erd-Nematoden mit besonderer Ber�cksichtigung der Steiermark und der Bukowina, zugleich met einer Revision s�mtlicher nicht mariner, freilebender Nematoden in Form von Genus-Beschreibungen und Bestimmungsschl�sseln. Archiv f�r Naturgeschichte A 87(1921), 1-650.
Phani, V., V.S.Somvanshi, U. Rao and M.R. Khan. 2019. Paratylenchus jasmineae sp. n. (Nematoda: Paratylenchinae) from rhizosphere of Jasminum sambac in India. Nematology 21:479-488.
Rhoades, H.L. and M.B. Linford. 1959. Molting of preadult nematodes of the genus Paratylenchus stimulated by root diffusates. Science 130: 1476-1477.
Raski, D.J. (1962). Paratylenchidae n. fam. with descriptions of five new species of Gracilacus n. g. and an emendation of Cacopaurus Thorne, 1943, Paratylenchus Micoletzky, 1922 and Criconematidae Thorne, 1943. Proceedings of the Helminthological Society of Washington 29, 189-207.
Raski, D.J. 1975. Revision of the Genus Paratylenchus Micoletzky, 1922 and Descriptions of New Species. Part I of Three parts. J. Nematology 7 :15-34.
Raski, D.J. 1975. Revision of the Genus Paratylenchus Micoletzky, 1922 and Descriptions of New Species. Part II of Three parts. J. Nematology 7 :274-295.
Raski, D.J. 1976. Revision of the Genus Paratylenchus Micoletzky, 1922 and Descriptions of New Species. Part III of Three parts--Gracilacus. J. Nematology 8:97-115.
Van den Berg, E., Tiedt, L.R. & Subbotin, S.A. (2014). Morphological and molecular characterisation of several Paratylenchus Micoletzky, 1922 (Tylenchida: Paratylenchidae) species from South Africa and USA, together with some taxonomic notes. Nematology 16, 323-358. DOI: 10.1163/ 15685411-00002769
Zhuo, K., X. Liu, Y. Tao, H. Wang, B. Lin and J. Liao. 2018. Morphological and molecular characterisation of three species of Paratylenchus Micoletzky, 1922 (Tylenchida: Paratylenchidae) from China, with a first description of the male P. rostrocaudatus. Nematology 20:837-850.