Heterodera		Contents		Rev 11/25/2008
cyst nematodes		Classification		Hosts
		Morphology and Anatomy		Life Cycle
Return to Heterodera Menu		Economic Importance		Damage
		Distribution		Management
Return to Heteroderidae Menu		Feeding		References
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Classification:

Tylenchida
       Tylenchina
        Tylenchoidea
         Heteroderidae
          Heteroderinae
           Heterodera (Schmidt, 1871)
    Synonyms:        
           Tylenchus (Heterodera) (Schmidt, 1871)
           Heterodera (Heterodera) (Schmidt, 1871)
           Heterobolbus (Railliet, 1896)
           Bidera (Krall' and Krall', 1978)
           Ephippiodera (Shagalina and Krall', 1978)

Refer to Subfamily Diagnostics (Heteroderinae) for taxonomic history and distinctions among related genera.

Slide show on Globodera and Heterodera spp.

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Morphology and Anatomy:

. Cyst of Heterodera glycines	Sexual dimorphism; female swollen; males vermiform. Female body forms a cyst.   Females: anterior neck-like region; swollen body shape - lemon, round, or pyroid shape (about 0.5-0.6 mm diam). Weak cephalic framework. Moderate stylet with small rounded knobs.   Metacorpus enlarged and fills neck region.   Diovarial; prodelphic; ovaries coiled or reflexed.   Vulva subterminal; anus terminal.  Posterior region important taxonomically: vulval cone vulva position presence or absence of bullae (blister-like internal projections of the body wall) fenestra - thinner areas in cuticle - may break down to allow juvenile emergence - bifenestrate, circumfenestrate, etc. Pre-parasitic stage: vermiform J2, 300-500 µm long. Heavily sclerotized head framework; head offset. Stylet prominent with anteriorly-directed knobs. Ventro-lateral overlap of esophageal glands over intestine. Genital primordia visible. Pointed tail. Post-parasitic stages: swollen. Stylet weak, sometimes not visible in 3rd and 4th stage.   Developing gonads visible.
Males: Vermiform, 1-1.5mm length.   Sclerotized cephalic framework, rounded head cap.   Strong stylet; knobs project forward.   Esophagus tylenchid, overlaps ventro-laterally.  Reproductive system monorchic. Curved spicules. No bursa. Tail bluntly rounded.  [Ref: H. Ferris.]

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Distribution:

Worldwide, usually with the definitive hosts of each species.

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Economic Importance:

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Feeding:

Juveniles enter root to region of developing vascular tissues by direct penetration of cells.   Juveniles may feed from individual cells as they cut through cell walls while migrating to permanent feeding site region.

The permanent feeding site is a syncytium which is stimulated in a cortical or endodermal cell.  The syncytium becomes multinucleate after 24 hours as adjacent cells merge.  Cell wall dissolution is through a combination of physical stress (nematode head movement) and chemical action.  

Syncytia associated with developing males are usually smaller than those associated with females.  

Large sectors of the developing root, including areas that would have become vascular tissue are transfomed into syncytia.  Syncytia have many plastids, mitochondria, ribosomes, increased rough endoplasmic reticulum and enlarged lobed nuclei.  There appears to be no synthesis of DNA and nuclear division probably does not occur.  

Cell wall protruberances increase the surface area of the cell membrane for flow of solutes from the xylem to the syncytium - the transfer cell configuration (Endo, 1975).

More than 50 genes are upregulated to some extent in the development of giant cells (Meloidogyne) and syncytia (Heterodera/Globodera) (Gheysen and Fenoll, 2002). Both types of feeding cells have the genome amplified as a result of multiple shortened cell cycles; but the processes differ. Giant-cells go through repeated (acytokinetic) mitosis.  Syncytia undergo repeated S-phase endoreduplication without mitosis or nuclear division. 

The eukaryotic cell cycle has four stages.: 1. Nuclear DNA is replicated during synthesis phase (S-phase). 2. DNA synthesis is followed by an interval called the G2 phase (G=gap). 3.  Mitosis occurs, the nucleus divides (M-phase). 4.  The interval between the completion of mitosis and the beginning of DNA synthesis is the G1-phase,  In normal cell division, the cell divides (cytokinesis) after the mitosis phase. In the root-knot nematode (Meloidogyne) feeding site there is repeated nuclear division (S and M phases of the cell cycle) but no cell division; this is called acytokinetic mitosis or karyokinesis without cytokinesis. In the cyst nematode (Heterodera, Globodera) feeding site, the S phase of the cell cycle is activated but not the M phase.   Instead, the cells repeatedly go through the S-phase (endoreduplication) and probably through parts of the  G1 and G2 phases, but bypass mitosis.

The Cell Cycle:  modified from Gheysen and Fenell, 2002.

Mundo and Baldwin showed that, in the Heteroderinae, syncytium formation and number varies with nematode species and genus in the same plant.

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Hosts:

Several forms of delayed hatch and diapause exhibited.  

1.  Host-mediated hatch in response to host root exudates.  Vary in degree of response to hatching factors:
         a) Very sensitive - hatch in water only 5% of that in host root 
            diffusate.
            G. rostochiensis, H. carotae, H. cruciferae, H. humuli
         b) Intermediate - hatch in water 10-50% of that in diffusate.
            H. schachtii, H. trifolii, H. galeopsidis.
         c) Insensitive - apparently not stimulated by diffusate.
            H. goettingiana, H. avenae, H. glycines.  H. avenae requires
            a chill period to break diapause.
Artificial hatching agents include Aminoacridine (Rivanol) and ZnCl for H. schachtii.
Ecological factors also influence hatch: temperature, moisture, aeration, 
osmotic potential, pH, etc.   

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Life Cycle:

J2 enters near root tip and takes position in cortex with head near vascular cylinder.  Moves intra- and intercellularly towards vascular tissues.  

During development, female breaks through cortex to surface so that most of the body of adult female remains outside root.  

Sugarbeet cyst nematode molts at 6, 12, and 15 days after entering root; matures in 19 days at 25 C.

Males are needed for reproduction in most species.  

Eggs are retained in cysts, but some are deposited in egg masses in many species.  Distended uterus enlarges to fill body; eggs are packed in mucoid mass. 

Cysts undergo a color change as they mature - from white to brown  - due to action of polyphenol oxidase on polyphenols in the cyst wall.  The wall remains permeable to chemicals and dissolved oxygen. 

Cyst drops-off of root when dead; mucoid packing disappears.

Life cycle diagram by Charles S. Papp, CDFA

       H. schachtii - about 2 generations per year in Europe.
                    about 3 generations per year in northern California.
                    about 5 generations per year in the Imperial Valley.
      H. glycines - about 5 generations per year in North Carolina.

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Damage:

Little mechanical injury due to the parasitism, body of female on outside of the root and no cell division stimulated.  

Branch rootlets may be stimulated near the point of infection.  

General debilitation and reduction in efficiency of the root system.  Chlorosis, stunted growth, wilted plants.

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Management:

Management strategies vary with species and biology.  

Management of this genus is usually difficult due to prolonged viability.  Possibilities include prevention, crop rotation, soil fumigation, use of resistant varieties, and use of clean seed sources.

1. Prevention/Exclusion: attempt to prevent spread, for example quarantine of potato growing areas of Long Island, New York.  Clean equipment before entry into field, but cysts can also be spread by wind and birds.
2. Crop rotation: sugarbeets grown once every 4 years in recommended rotation sequence in southern California.  Dutch regulatory agencies monitor potato fields.  Potatoes may not be grown more than twice, longer rotation in infested fields.
3. Soil fumigation: reduces populations to low levels, but does not 
              eradicate.
4. Resistant cultivars: available for some crops.  Progress has been made on  varieties of sugarbeets resistant to H. schachtii.
5. Clean seed sources: Cysts are readily introduced in infested planting stock or seed.

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References:

H. Ferris

Endo, B. 1976. In Vistas on Nematology

Gheyson, G. and C. Fenoll.  2002. Gene expression in nematode feeding sites.  Ann. Rev. Phytopathol. 40: 191-219.

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Copyright © 1999 by Howard Ferris.
Revised: November 25, 2008.