Plant Parasitic
Nematodes

AN INTRODUCTION

 
 
 
 
 

Webmaster: Daniel Snyder

Last Edited: May 30, 2002

 

Genus Heterodera

The Cyst Nematode

Most important species:

  • H. glycines (soybean cyst - #1 pathogen of soybean)
  • H. schachtii (sugar-beet cyst nematode; 218 host species)
  • H. avenae (cereal cyst nematode)
  • H. trifolii (clover cyst nematode)

General characteristics

  • limited host-range
  • reproduce by amphimixis
  • form complex feeding sites called "syncytia"
  • cysts are lemon-shaped

Life Cycle

  • J2 cuts slit in egg shell with stylet(no enzymes involved)
  • J2 migrates to root zone of elongation and penetrates to vascular cylinder
  • feeding site(syncytium) is initiated and J2 molts to sedentary J3
  • adult female produces 200-600 eggs that mature in the cyst
  • some species produce an egg mass for spontaneous hatching
  • eggs retained in cysts overwinter or survive up to 30 years(G. pallida)
  • hatching is often stimulated by hatching factors (root exhudates)

Hots parasite interactions

  • intracellular migration of J2 causes necrosis mechanically and with cellulases
  • syncitia are formed in pericyle and endodermal cells by dissolution of cell walls
  • this syncytial initial is formed by the excretion of esophageal compounds
  • multinucleate cells result from the coalescence of neighboring cells
  • nuclei enlarge and cytoplasm becomes granulated
  • the syncitium shows increased metabolism in response to the nematode which is acting like a nutrient sink in the infected roots
  • feeding tubes form from nematode and plant secretions in the syncitium at the distal tip of the stylet, but are not enveloped by endoplasmic reticulum as in root-knot feeding tubes
  • a feeding plug is also formed at the point of cell wall penetration
  • no galling due to the lack of hyperplasia and hypertrophy
  • degradation of the syncitium results in considerably more necrosis than root-knot

APSnet articles on cyst nematodes.

Broken cyst with eggs Cysts on roots Juveniles hatching from cysts

Left to right: broken cyst with eggs, cysts on roots, juveniles hatching from cysts