Pratylenchus

 

Contents

 

Rev 01/24/2020

 lesion nematodes Classification Hosts
Morphology and Anatomy Life Cycle
Return to Pratylenchus Menu Economic Importance Damage
Distribution Management
Return to Pratylenchidae Menu Feeding  References
    Go to Nemaplex Main Menu   Go to Dictionary of Terminology

Classification:

Tylenchida
       Tylenchina
        Tylenchoidea
         Pratylenchidae
          Pratylenchinae

          Pratylenchus (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 than 70 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.

Back to Top

Morphology and Anatomy:

Nematodes in this genus are 0.4-0.5 mm long (under 0.8 mm).

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).   

Males:  Have caudal alae (bursa) enveloping tail.

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.

Body size range for the species of this genus in the database - Click:

Morphometric Key to the Nine Common Pratylenchus Species in California

1.
   
   
2
Bisexual species, sperm in most spermatheca, males common. 7
2. Very large, round stylet knobs, stylet averages 19 µm in length; V% 82-89; 2 lip annules P. brachyurus
Stylet knobs oval or flattened, stylet generally less than 19 µm long 3
3. Tail tip annulated, 3 lip annules P. crenatus
Tail tip smooth 4
4 Lip annules 2 5
Lip annules 3 6
5 Average V%=84, lip annules about same width; stylet knobs often flattened; vulval lips somewhat smooth P. neglectus
Average V%=78%, anterior lip annules markedly narrower than posterior; vulval lips protrude somewhat P. scribneri
6 Tail normally truncate, stylet averages 18 µm in length;  V% averages 76; normally assumes a "J" or "C" shape when heat killed P. zeae
Tail narrowly rounded, stylet averages 16 µm in length;  V% averages 71; normally almost straight when heat killed P. thornei
7 Lip annules 2, occasionally 3 on one side P. coffeae
Lip annules 3, occasionally 4 on one side 8
8 Spermatheca normally round, posterior uterine branch 1 to 1.5 body widths long; large stylet knobs P. penetrans
Spermatheca normally oval, posterior uterine branch generally greater than 2 body widths long; moderate sized stylet knobs P. vulnus
 
Back to Top

Distribution:

Members of this genus are distributed worldwide; individual species are influenced by climate.

Back to Top

Economic Importance:

C- and D-rated pests in California.

Back to Top

Feeding:

Migratory endoparasites.  

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 in cortex, but not exclusively.

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.      

Back to Top

Hosts:

Most species have quite wide host ranges.   

For an extensive host range list for this genus, click
Back to Top

Life Cycle:

For Ecophysiological Parameters for this genus, click 
 

Sexual reproduction probably occurs in those species where males are numerous.  Fewer than 50% of the described species are recognized asd having males so parthenogenicity is common in the genus.

Eggs laid singly in roots and soil; second stage hatches from egg.

Nematodes in soil and roots, lesions in roots.

Back to Top

Damage:

Actual damage caused by nematode feeding is difficult to ascertain because of associated organisms and secondary infections.

Back to Top

Management:

Back to Top

References:

Castillo, P. and Vovlas, N. 2007. Pratylenchus (Nematoda: Pratylenchidae): diagnosis, biology, pathogenicity and msanagement. Nematology Monographs and Perspectives 6.

Luc, Rev. Nematol. 10:203-218 (1987)

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.

Back to Top

Copyright 1999 by Howard Ferris.
Revised: January 24, 2020.