Fusarium Yellows of Sugarbeet

PP-1247, December 2003

Mohamed F. R. Khan, Extension Sugarbeet Specialist
North Dakota State University and University of Minnesota

Carl A. Bradley, Extension Plant Pathologist,
North Dakota State University

Carol E. Windels, Professor of Plant Pathology, University of Minnesota
Northwest Research and Outreach Center, Crookston

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Fusarium yellows of sugarbeet was identified in the Red River Valley in a few fields located between Moorhead, Minnesota and Drayton, North Dakota in 2002. Fusarium yellows is caused by the fungus, Fusarium oxysporum f. sp. betae, although other Fusarium species can be involved as secondary invaders. The disease causes significant reduction in root yield and recoverable sucrose. In storage, quality of infected roots may deteriorate more rapidly than in non-infected roots.

Symptoms

Fusarium yellows first appears on older leaves as chlorosis (yellowing) between the larger veins. As the disease progresses, younger leaves also become chlorotic, and the older, symptomatic leaves become necrotic (Figure 1). Occasionally, only half a leaf is chlorotic or necrotic (Figure 2) (a symptom more typical of Verticillium wilt, which also was recently identified on sugarbeet in this region). In early stages of the disease, foliage tends to wilt during the day but recovers overnight. Entire leaves eventually die but remain attached to the plant and collapse in a heap around the crown.There are no external root symptoms. A transverse section through the root shows a grayish brown vascular discoloration (Figures 3-5). Mature plants rarely die, but yield is reduced.

	Figure 1. Lower, older leaves become yellow between the larger veins, and eventually die but remain attached to the plant.
	Figure 2. Some plants infected with Fusarium may have half a leaf with necrosis.
	Figure 3. Infected root with grayish-brown to black discoloration of vascular bundles.
	Figure 4. Outer surface of infected root shows no symptoms. Transverse section through the root shows grayish-brown to black discoloration.
	Figure 5. Disintegration of cells in the vascular tissue in advanced stage of the disease.

 

Biology

Fusarium oxysporum f. sp. betae survives in soil and plant residues as spores, chlamydospores, or mycelium. When conditions are favorable, the fungus enters sugarbeet roots and invades the vascular system where it produces toxins that are transported upward in the plant, causing foliar symptoms. The fungus also acts as a "plug" that clogs the vascular tissue, and subsequently causes wilting. The disease is favored by high soil temperatures -- above 75°F; symptoms typically do not appear early in the growing season. Fields that are waterlogged or with poor soil structure provide favorable conditions for infection. The fungus survives in soil for many years. Nematode infection will often increase severity of Fusarium wilt. Fortunately, nematodes have not been identified on sugarbeet grown in Minnesota and North Dakota.

Management

Crop rotation may reduce inoculum buildup in the soil but this practice is unreliable because F. oxysporum f. sp. betae has a wide host range and chlamydospores survive for many years. Movement of infested soil on contaminated field equipment should be avoided to prevent spread to non-infested fields. Because the disease is new to the Red River Valley, other methods of managing the disease are not currently available. Identification and development of resistant varieties will be an important step in managing this disease in the Red River Valley.

Photo credits

Figures provided by C. A. Bradley, M. F. R. Khan, and R. Nelson.

Selected References

Duffus, J. E. and Ruppel, E. G. 1993. Diseases. Pages 346-427 In: The sugar beet crop. D. A. Cooke and R. K. Scott (Eds.) Chapman and Hall, London.

Franc, G. D., Harveson, R. M., Kerr, E. D. and Jacobsen, B. J. 2001. Disease management. Page 131-160 In: Sugarbeet Production Guide. Univ. Nebraska Coop. Extension EC01-156.

Schneider, C. L. and Whitney, E. D. 1986. Fusarium Yellows. Page 18 In: Compendium of Beet Diseases and Insects. E. D. Whitney and J. E. Duffus (Eds.). APS Press, St. Paul, MN.

For more information on this and other topics, see: www.ag.ndsu.nodak.edu

PP-1247, December 2003