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.