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%