Plant Parasitic
Nematodes

AN INTRODUCTION

 
 
 
 
 

Webmaster: Daniel Snyder

Last Edited: May 30, 2002

 

Genus Meloidogyne

Root-knot Nematodes

Most important species:
M. incognita, M. arenaria, M. hapla and M. javanica

  • root knot nematodes cause more damage worldwide than any other genus
  • some species can parasitize more than 2,000 plant species
  • form complex feeding sites in root called "giant cells"
  • galls are formed on root
  • reproduce by parthenogenesis
  • eggs laid outside the female body in a gelatinous matrix sac that often protrudes to the surface of the root and can be seen on the root surface as a sign
  • 500-1000 eggs laid per female

At the establishment of a feeding site several dramatic physiological changes occur in both the host plant and the developing nematode including:

  • secretion of esophageal gland products possibly including hormones and enzymes required for feeding site formation and maintenance
  • degeneration of longitudinal muscles of J2 rendering nematode immobile(sedentary)
  • basal zone of the cuticle breaks down allowing for swelling during feeding
  • males third molt is a true metamorphosis seen in greater numbers under adverse environmental conditions by female sex differentiation(reversal)
  • undifferentiated vascular cells are targeted for feeding site initiation, most likely these are xylem parenchyma cells
  • feeding cells increase in size up to 100%(hypertrophy)
  • cell contents multiply including mitochondria and nuclei(40-100 per cell)
  • walls develop elaborate ingrowths and become thickened possibly to provide better absorptive abilities to meet the nutritional demands of the growing nematode
  • giant cells degenerate upon nematode death, suggesting required stimulation by nematode for maintenance

Gall formation is a visible sign of root-knot nematode infection resulting from the hypertrophy and hyperplasia indicative of feeding site formation within the roots.

(1975-1984) The International Meloidogyne Project was conducted to assess the worldwide impact of this genus on agriculture and was based here at NCSU.

Some of the results of this project include:

  • The North Carolina Differential Host Range Test
  • Frequencies of the most common species:
    - M. incognita (Southern root knot nematode) 54%
    - M. javanica (Javanese root knot nematode) 30%
    - M. hapla (Northern root knot nematode) 7%
    - M. arenaria (peanut root knot nematode) 7%

Picture 1. First juvenile molt inside egg.

First juvenile molt inside egg

Picture 2. Infection cycle of RKN.

J2 free in soil J2 penetrating root J2s migrating to the vascular cylinder Adult female with 'giant cells' surrounding her head

A -----------------> B-----------------> C----------------> D

A) J2 free in soil, B) J2 penetrating root, C) J2s migrating to the vascular cylinder

D) Adult female with 'giant cells' surrounding her head

Picture 3. Root-knot Nematode disease cycle

Root-knot Nematode disease cycle