| Root lesion nematode |
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| Pratylenchus penetrans |
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Plant hosts
Studies show that at least 55 weeds species, including many the common weeds, are hosts of root-lesion nematodes (Pratylenchus penetrans). Some common weeds are lambsquarters, redroot pigweed, common purslane, common chickweed, wild mustard, fireweed, wild carrot, common milkweed, field bindweed, common plaintain, goldenrod, common ragweed, common groundsel, Canada thistle, Scotch thistle, chicory, and common dandelion.
To view larger image click on picture.
Image provided by Clemson University USDA Extension slide series.
Means of movement and dispersal
Plant parts liable to carry the pest in trade and transport:
- Bark: eggs, juveniles and adults, all of which are born internally and visible under light microscope.
- Bulbs, tubers, corms, and rhizomes: eggs, juveniles and adults all of which are born internally and visible under light microscope.
- Seedlings and micropropagated plants: eggs,juveniles and adults all of which are born internally and visible under light microscope.
- Roots: eggs, juveniles and adults all of which are born internally and visible under light microscope.
- Stems: eggs, juveniles and adults all of which are born internally and visible under light microscope.
Plant parts not known to carry the pest in trade and transport:
- Fruits.
- Growing medium accompanying plants
- Flowers.
- Leaves.
- Seeds.
- Wood.
Symptoms
The principal symptom of P. penetrans activity is the presence of distinctive lesions on host plant feeder roots. Other species of the genus may also cause lesions but the discoloration may be less intense. The lesions, sometimes described as resembling 'cat scratches', usually appear as discolored yellowish to brownish elongate marks parallel to the long axis of the root. They are formed as the nematode tunnels along a series of cortical cells, moving through the end-walls from cell to cell and feeding on the contents. Roots damaged from severe lesioning are generally discolored, frequently yellow-brown or 'rusty'. Root systems affected by the nematode may show either 'witches-broom' clusters of proliferated feeder roots, or feeder roots may be sparse in comparison with normal root systems as a result of root-terminal meristem killing. Aboveground plant organs do not show symptoms specific to this nematode. Commonly, leaves will appear chlorotic, pale-green to yellowish; plants will be stunted and weak, with a tendency to wilt in drought situations; and fruit may be undersized. Field and vegetable crops may exhibit patches of plants with poor growth and reduced yields. Symptoms such as twig dieback can be caused by P. penetrans, but may also be caused by other pathogens. Likewise, secondary root rots may result from the invasion of bacteria or fungi into entry wounds left by the nematode. Premature senescence of plants can also result from P. penetrans attack, but is not specific.
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