Rev 01/08/2024
Tylenchida Tylenchina Tylenchoidea Pratylenchidae Pratylenchinae
Pratylenchus Filipjev, 1936
Type species of the genus: Pratylenchus pratensis (de Man, 1880) Filipjev, 1936 Synonyms: None.
The genus name is derived a a contraction of the words pratum (Latin= meadow), tylos (Greek= knob) and enchos ( Greek=spear).
Originally described as Tylenchus pratensis by De Man in 1880 from a meadow in England. Pratylenchus scribneri was reported from potato in Tennessee in 1889.
Root-lesion nematodes of the genus Pratylenchus are recognised worldwide as major constraints of important economic crops, including banana, cereals, coffee, corn, legumes, peanut, potato and many fruits. Their economic importance in agriculture is due to their wide host range and their distribution in every terrestrial environment on the planet (Castillo and Vovlas, 2007).. There are more taround 100 described species, fewer than half of them are known to have males..
Morphological identification of Pratylenchus species is difficult, requiring considerable subjective evaluation of characters and overlapping morphomertrics. Molecular techniques are increasingly important.
RFLP techniques have been used as a diagnostic method for Pratylenchus agilis, P. bolivianus, P. brachyurus, P. coffeae, P. crenatus, P. fallax, P. goodeyi, P. loosi, P. mediterraneus, P. neglectus, P. penetrans, P. pratensis, P. pseudocoffeae, P. scribneri, P. subranjani, P. thornei, P. vulnus and P. zeae. The species could be differentiated by a combination of at least two enzymes. CfoI differentiated all nematode species with the exception of P. fallax, P. penetrans and P. pseudocoffeae. P. fallax was separated by a DdeI restriction, and P. pseudocoffeae by a PstI digestion (Waeyenberge et al, 2000).
Castillo and Vovlas (2007) provide an excellent comprehensive review of the genus.
No sexual dimorphism in the anterior part of the body.
Deirids absent.
Lip area low, flattened anteriorly, not offset, or only weakly offset, from body contour. SEM reveals that lip area is characterized by fusion of labial disc with submedial lip sectors; lateral lip sectors not reduced.
Esophageal glands overlapping intestine ventrally for a moderate distance. Esophago-intestinal valve not well developed.
Phasmids located at mid-tail or slightly posterior.
Female: Genital tract monovarial with posterior branch reduced to a post-uterine sac.
Female is slender.
Tail 2 to 3 times the anal body diameter, terminus rounded (rarely pointed).
Gubernaculum plain, not protruding.
[Ref: Luc, (1987) and H. Ferris.]
Distinguishing the species of Pratylenchus based on morphometric characters is not easy but may be important as a basis for management decisions that include resistant varieties, cover crops and crop rotation.
Morphometric Key to the Nine Common Pratylenchus Species in California
Members of this genus are distributed worldwide; individual species are influenced by climate.
C- and D-rated pests in California.
Damaging to a wide range of plant species. As an example, crops affected by various Pratylenchus spp. include different species of the Musaceae family, including plantain (Musa paradisiaca [L.] and banana (Musa acuminata), in which the nematode damages the root system (Riascos-Ortiz et al., 2022). Symptoms induced by the nematode in Musaceae roots are internal root lesions that are initially yellow and later turn purple and finally brown. Externally, the necrotic areas of the roots appear black due to the destruction of the cortical tissues (CABI, 2022). In affected plantain and banana plants, the nematode reduces the root system and the ability to take up water and nutrients, which causes foliar chlorosis, growth retardation, decreased bunch weight, lengthening of the productive cycle, and returns or weak suckers (De Luca et al., 2012). In fields severely infested with the nematode, plants suffer toppling and complete bunch loss (CABI, 2022).
Similar effects of damaged root systems are reported for a range of crop species.
Migratory endoparasites of plant roots.
No distinct infective stage, adults and juveniles of all stages move in and out of roots, entering behind zone of elongation but may feed externally at root tip.
Feeds on parenchyma cells, largely but not exclusively in the root cortex. They enter the roots behind the zone of elongation, but may feed ectoparasitically as well, near the root tip
Move into root by pushing epidermal cells apart, or moving directly through them.
Inserts stylet into cortical cells and withdraws contents associated with pulsating of metacorpus.
Access provided for other pathogens by channels left in cortex.
They are polyphagous, migratory root endoparasites. Developing and reproducing in the soil or roots, they cause root lesion disease on many plant taxa in temperate and tropical regions around the world. Adults and juveniles of all stages are infective, moving in and out of roots. They feed on parenchyma cells, largely but not exclusively in the root cortex. They enter the roots behind the zone of elongation, but may feed ectoparasitically as well, on the outside at the root tip.
Most species have quite wide host ranges.
Parthenogenicity is common in the genus and many species are not known to have males. Fewer than 50% of the described species are recognized asd having males so parthenogenicity is common in the genus.
Adults and juveniles of all stages are infective, moving in and out of rootsSexual reproduction probably occurs in those species where males are numerous.
Eggs laid singly in roots and soil; second stage hatches from egg.
Nematodes in soil and roots, lesions in roots.
Actual damage caused by nematode feeding is difficult to ascertain because of associated organisms and secondary infections. For example, in addition to the direct damage caused to plantain and banana roots, by sveral Pratylenchus spp., there is a high correlation between Pratylenchus infection and infection by fungi such as Fusarium oxysporum, F. redolens, F. sambucium, Nigrospora musae, and Rhizoctonia solani, and also bu bacteria such as Xanthomonas campestris (Bridge et al., 1997; Arboleda-Riascos et al., 2022).
Confounding the problem is that microscopic identifiaction of some species is difficult due to overlap of morphological am morphometric characteristics. In such cases, a clear separation of species requires molecular analyis (De Luca et al., 2012; Arboleda-Riascos et al., 2022).
Nematodes of the genus Pratylenchus were first reported in California in 1927, but their significance as plant pathogens was not recognized until investigations conducted from 1930 to 1943 revealed damages caused by root lesion nematodes to walnut, fig, and cherry trees. At that time, confusion over species identities, distribution, and host ranges made it difficult for state and county regulatory agencies to restrict the spread of root lesion nematodes until the group was revised by Sher and Allen in 1953.
By 1959, P. brachyurus, P. penetrans, P. vulnus, P. scribneri, and P. hexincisus were recognized as root lesion nematodes of economic importance in California (Chitambar et al., 2018).
Australasian Plant Pathology Society Factsheets on Plant-parasitic Nematodes (Prepared by Dr. Graham R. Stirling)
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CABI. 2022. Pratylenchus coffeae (banana root nematode). Invasive species compendium. Datasheet, https://www.cabi.org/isc/datasheet/43895.
Castillo, P. and Vovlas, N. 2007. Pratylenchus (Nematoda: Pratylenchidae): diagnosis, biology, pathogenicity and msanagement. Nematology Monographs and Perspectives 6.
De Luca, F., Troccoli, A., Duncan, L., Subbotin, S., Waeyenberge, L., Coyne, L., Brentu, F., and Inserra, R. 2012. Pratylenchus speijeri n. sp. (Nematoda: Pratylenchidae), a new root-lesion nematode pest of plantain in West Africa. Journal of Nematology 14:987�1004.
Luc, Rev. Nematol. 10:203-218 (1987)
Riascos-Ortiz, D., Mosquera-Espinosa, A. T., Var�n de Agudelo, F., Oliveira, C. M. G., and Mu�oz Fl�rez, J. E. 2022. Non-conventional management of plant-parasitic nematodes in Musaceas Crops. Pp. 381�422 in K. K. Chaudhary, M. K. Meghvansi, eds. Sustainable management of nematodes in agriculture, vol. 1: Organic management. Sustainability in Plant and Crop Protection, vol. 18. Cham: Springer.
Sher, S. A., and Allen, M. W. 1953. Revision of the genus Pratylenchus (Nematoda: Tylenchidae). University of California Publications in Zoology, 57, 441�447.
Waeyenberge, L.; Ryss, A.; Moens, M.; Pinochet, J.; Vrain, T.C. 2000. Molecular characterisation of 18 Pratylenchus species using rDNA restriction fragment length polymorphism. Nematology 2: 135-142.