Root Knot Nematode

Root-knot nematodes (Meloidogyne spp.) are capable of reproducing on over 2,000 species of plants (including most vegetable crops) and are responsible for approximately 50% of overall nematode damage worldwide. Symptoms of plant infestation by root-knot nematodes may include knot- or gall-like formations on the roots. These knots, or galls, inhibit the ability of the root to take up nutrients and water. Knot formation is due in large part to the development of specialized feeder cells called “giant cells”.

The relationship between the plant and nematode is complex and not well understood. This complex interaction begins when an infective second-stage juvenile (J2) locates and penetrates a root behind the root cap in the zone of elongation or at rupture sites of lateral roots. Upon entering the root, the J2 migrates to the central cylinder region and begins to establish a feeding site. How the nematode chooses where to set up a feeding site is unknown, but its choice is probably due to specific plant signals or cues.  Once the feeding site is set up the nematode will feed sequentially from the cells that make up the feeding site.  It takes about 30-45 days (condition dependent) for nematodes to mature.  Females can lay up to 1000 eggs, with multiple generations in one cropping season.

​Substances, initially produced in the dorsal and subventral pharyngeal glands of the nematode, are injected into the plant cells that surround the head of the nematode to initiate the feeding site. These undifferentiated root cells (normally four to six cells) undergo a remarkable morphogenesis into a feeding structure consisting of several giant, multinucleated cells with many of the hallmarks of transfer cells. Transfer cell-like characteristics of giant cells include: large numbers of mitochondria and plastids, numerous small vacuoles, dense cytoplasm, and thickened and invaginated cell walls with a continuous plasma membrane.

In addition to remodeling of the cells to create giant cells, an extensive remodeling of vascular tissues also occurs.  Extensive alterations in the vascular tissues with proliferation of phloem and xylem elements envelops the giant cells.  Though the feeding site does not directly connect to the vascular tissues nutrients are delivered to the giant cells via membrane bound transporters.

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