Fig. 1. Severe root-knot nematode infestation on fibrous roots of a plant of Jewel. The stem of this plant is also affected by Fusarium stem canker.
Fig. 2. Typical bumps on storage roots of Beauregard with root-knot nematode. Two bumps on the lower root were sliced to reveal the presence of swollen female nematodes in the dark spots.
Root-knot nematode, Meloidogyne spp., is widely distributed throughout the world and can cause significant damage, especially in sandy soils. It affects both the feeder roots and the storage roots.
On the feeder roots, the nematode induces galls that tend to be smaller on sweet potatoes than on many other crops. On these galls are egg masses than can contain more than 500 eggs (Fig. 1).
Effects on storage roots vary among cultivars. Cracking occurs commonly on some cultivars such as Centennial, and these cracks are quickly invaded by fungi that cause rots. On Beauregard, cracking does not normally occur, but instead little bumps or pimple-like protuberances appear (Fig. 2).
Swollen female nematodes, sometimes with egg masses, can be found embedded in the storage root beneath each bump or crack.
Please direct questions or comments about sweet potato diseases to Chris Clark.
7/27/2005 7:13:50 PM
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