Bacterial Wilt of Alfalfa

Bacterial Wilt of Alfalfa

Bacterial wilt commonly occurs throughout the most of the alfalfa growing areas of the world. The disease is caused by Clavibacter michiganensis subsp. insidiosus (McCulloch) Davis et. al. = Corynebacterium insidiosum (McCulloch) Jensen. The bacterium survives in plant material in the soil, hay and seed for several years. It can be spread plant to plant via surface water (rain) irrigation and contaminated implement. Long distance spread is attributed to contaminated seed and hay. Bacterial wilt is most common on plants growing in low, poorly drained areas of the field. It is also more common in wet years. Primary infection occurs when bacteria enter roots via wounds. Wounding can be caused by insect or nematode feeding, winter injury of mechanical injury. The bacterium is also spread to actively growing plants during harvest when newly cut stems provide a port of entry for the bacterium. Once the bacterium enters the plant, symptoms are slow to develop, usually visible in the second or third crop year. C. michiganensis subsp. insidiosus colonizes the vascular and disrupts water transport by clogging vessels with vast numbers of bacterial cells and production of a phytotoxic glycopeptide. Two nematodes, the northern root knot nematode (Meloidogyne hapla Chitwood) and the stem nematode (Ditylenchus dipsaci (Kuhn) Filipjev) have been shown to have an influence on disease development. The interaction between the northern root knot nematode and C. michiganense subsp. insidiosum results in increased incidence and severity. The stem nematode is a vector of the pathogen and increases host susceptibility.

Symptoms

Symptoms are produced on plants scattered randomly in field. Infected plants initially wilt during periods of moisture stress then recover. As the disease progress affected plant are visible from a distance as being yellow and slightly dwarfed or straw-colored and dead. Infected plants do not grow well after the first cutting. They produce small leaves and are bunchy in appearance. Plants with less severe infection are dwarfed and yellow and have leaves that are thickened and cup upward or curl. Severely infected plants exhibit these symptoms to a greater degree and eventually die. When the outer bark is peeled away, the outer vascular tissue of infected crowns and taproots has a yellow to brown discoloration. This area appears as a yellow ring when a cross section is made. There may also be discolored pockets of infection under the bark. The vascular tissue eventually becomes completely discolored and rots. Plants that are not killed outright are more susceptible to winter injury.

Plant Health Management

Plant Resistant Cultivars

Do not mow when plants are wet.

Harvest healthy stands first

References

Cormack, M.W. 1961. Longevity of the bacterial wilt organism in alfalfa hay, pod debris, and seed. Phytopathology 51:260-261.

Hawn, E.J. 1971. Mode of transmission of by Ditylenchus dipsaci. J. Nematol. 3:420-421.

Hunt, O.J., Griffin, G.D., Murray, J.J., Pedersen, M.W., and Peaden, R.N. 1971. The effects of root knot nematode on bacterial wilt in alfalfa. Phytopathology 61:256-259.

Nyvall, R.F. 1989. Field crop diseases handbook, 2^nd ed. Van Nostrand Reinhold, New York, NY. 817pp.

Ries, S.M. and Strobel, G.A. 1972. Biological properties and pathological role of a phytotoxic glycopeptide from Corynebacterium insidiosum. Physiol. Plant Pathol. 2:133-142.

Stuteville, D.L. and D.C. Erwin eds. 1990. Compendium of alfalfa diseases, 2^nd ed. American Phytopathological Society. St. Paul, MN. 84 pp.

Useful Links

Oregon State University

Oregon State University 2

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Caveat

This description is presented for information only and no endorsement is intended for products listed, nor criticism meant for products not mentioned. Always consult the product label before purchasing and using any pesticide.

Material contained on the Links from the page are the responsibility of the linked page's author(s).

This page was researched drafted by: Jane Christensen, Department of Plant Pathology, University of Nebraska-Lincoln

Disease images were provided by: Dr. David Wysong, Department of Plant Pathology, University of Nebraska-Lincoln

Questions, Comments, Complaints and Complements?

This page is authored and maintained by:
Dr. J.E. Partridge, Department of Plant Pathology, University of Nebraska-Lincoln

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