HPIPM:Fusarium Wilt DB

Author: Howard F. Schwartz, David H. Gent, Gary D. Franc and Robert M. Harveson

Taxonomy

Domain	Eukarya
Kingdom	Fungi
Phylum	Ascomycota
Subphylum	Pezizomycotina
Class	Sordariomycetes
Subclass	Hypocreomycetidae
Order	Hypocreales
Family	Nectriaceae
Genus	Fusarium
Species	Fusarium oxysporum

Scientific Name

Fusarium oxysporum f.sp. phaseoli

Common Name

Fusarium wilt

Identification and Life Cycle

Fusarium wilt or yellows is caused by the fungus Fusarium oxysporum f. sp. phaseoli. The Fusarium wilt fungus occurs in most cultivated soils of the region where beans have been grown previously, and most plants grown in these soils will become infected to some degree before they mature. Disease severity is favored by high temperature stress and soil compaction. In general, any factor which contributes to a reduced rate of root growth increases the plant's susceptibility to Fusarium wilt. Early planting in cool, moist soil favors the disease. High plant populations also increase plant stress and favor infection. Improper cultivation, other soil-borne pathogens, and various herbicides are also known to induce injury of young roots and aggravate Fusarium wilt damage. The effect of Fusarium wilt is most apparent during blossoming and early pod set when the plant and its productivity are more sensitive to stress. Fusarium wilt infection is more apparent than that of Fusarium root rot, which seldom kills the plant. However, wilt infection may kill plants before or even after pod set. Both fungi can cause infected plants to mature two to three weeks earlier than normal. The pathogen is disseminated within and among fields by the movement of contaminated soil by wind, irrigation water, and on equipment. The pathogen can survive between dry bean crops as dormant chlamydospores or in infested crop debris.

Plant Response and Damage

Above-ground symptoms of Fusarium wilt appear on lower leaves which exhibit yellowing and wilting; this becomes more pronounced and progress upward into younger leaves. Stunting is evident, especially if plant infection and stress occurred during the seedling and vegetative stages. The margins of infected leaves turn tan to brown and diseased plants become progressively more yellow. Severely infected plants exhibit permanent wilting and premature defoliation. Vascular discoloration on the main stem is the diagnostic symptom and is usually evident after the initial appearance of foliar symptoms. The reddish brown vascular discoloration of root, stem, and petiole tissue of infected plants will vary considerably in intensity, depending on variety reaction, severity of infection and environmental conditions. Yield losses may approach 100% if susceptible varieties are grown in fields with a history of severe Fusarium wilt.

Biological Control

Incorporation of organic matter may reduce Fusarium wilt by improving soil tilth and water holding capacity.

Cultural Control

Plant high quality seed in warm (greater than 60°F), well-prepared seedbeds under conditions favorable to rapid seedling emergence. Resistant varieties are available and should be planted. Avoid planting in fields with a history of root rot problems. A three-year or longer rotation to non-hosts such as small grains or corn reduces root rot severity. Chiseling (sub-soiling) 10 to 20 inches deep between dry bean rows promotes root penetration and improves plant tolerance to wilt and root rot, but avoid root injury during field operations. Manage irrigation to eliminate moisture stress to the developing plant, but avoid excess water that may deprive roots of oxygen. Avoid dense plantings. Space plants at least two to three inches apart within the row to reduce plant competition for water. Till soil up around the base of infected plants to enhance lateral root development above infected portions of the hypocotyl.

Chemical Control

Fumigation reduces Fusarium wilt, but is expensive and seldom is cost effective.

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