| Bacterial wilt |
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| Clavibacter michiganensis |
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Plant hosts
- Major hosts: Lotus corniculatus (bird's-foot trefoil), Medicago falcata (yellow alfalfa), Medicago sativa (lucerne), Trifolium (clovers)
Click on image to view larger photo.
Image provided by J.D. Janse, Plant Protection Service, Netherlands.
Means of movement and dispersal
Plant parts liable to carry the pest in trade and transport:
- Leaves: bacteria is born internally and externally and is visible to naked eye.
- Roots: bacteria is born internally and externally and is visible to naked eye.
- Stems: bacteria is born internally and externally and is visible to naked eye.
Plant parts not known to carry the pest in trade and transport:
- Bulbs, tubers, corms and rhizomes.
- Fruits.
- Flowers.
- Wood.
Symptoms
Infected plants are usually scattered throughout a stand and are easily detected by their yellow-green colour and stunted growth. Mild symptoms consist of leaf mottling with slight cupping or upward curling of the leaflets and some reduction in plant height. Severely infected plants are stunted and yellow-green, with many spindly stems and small, distorted leaflets. Diseased plants are most evident in the regrowth after clipping (Jones and McCulloch, 1926; Close and Mulcock, 1972; Graham et al., 1979; Martens et al., 1984). Cross sections of the taproot show a yellowish-brown discolouration of the outer vascular tissue; as the disease progresses, the entire stele discolours. When the bark is peeled away the stele is yellowish brown, in contrast to the white of healthy plants. Pockets of infection sometimes appear on the inner surface of the bark (Jones and McCulloch, 1926; Close and Mulcock, 1972; Graham et al., 1979; Martens et al., 1984).
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