Fusarium oxysporum f. sp. radicis-lycopersici

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. lycopersici

Common Name

Fusarium wilt

Author: Jiaming Yu, University of Florida

Reviewed by: Jeffrey Rollins, University of Florida

Pathogen

Fusarium crown and root rot of tomatoes (Lycopersicon esculentum Milller) is caused by Fusarium oxysporum f. sp. radicis-lycopersici (FORL) Jarvis & Shoemaker. The fungus was first reported in Japan in 1969. It is one of the most destructive diseases of tomatoes (1, 2, 3). There is no distinguished physiological race of FORL. However, nine Vegetative Compatibility Groups (VCGs) have been identified, which indicates it has a high genetic diversity. There is no known teleomorph (4).

Symptoms and Signs

In general, symptoms include yellowing, wilting, stunted growth, and discolored internal stem tissue. The oldest leaves first begin to yellow while the fruit is reaching maturity. Eventually those yellow leaves turn brown. During the warmest times of the day, infected plants wilt and then recover at night. Sometimes, adventitious roots may occur above the infected parts. Severe infections can cause root damage, rapid wilting, and death. Plants can survive less severe infections through the growing season, but the fruit is often pale (2, 3).

Signs include yellow to orange or pinkish masses of macroconidia on lower stems and stem lesions. This is the asexual sporulation layer of the pathogen (2, 3).

Ecology and Spread

FORL is widespread and leads to substantial yield losses in both greenhouse and soil production systems. The pathogen is disseminated via infected seeds, plant material, and soil compost. Fungus gnats have been reported as vectors of the fungus. Readily spread conidia in water sources provide another way of pathogen dissemination, especially in irrigation and hydroponic cultivation system. Microconidia have been detected for airborne dispersal. The fungus enters through wounds or natural opening caused by secondary roots, and then colonizes the cortical tissue. At this phase, brown lesions are formed. In vascular tissues, the fungus can spread up to 25 cm. The optimum conditions for disease development is 50-68 F, low substrate pH, and soggy and ammoniacal soil (1, 2, 3). Once the root system is infected by this pathogen, the root system will be reduced. While the temperature increases, water demand increases dramatically which leads to plant wilt or death (4).

Geographic Distribution

Crown and root rot of tomatoes is a widely distributed disease in Western Europe, North America, the Mediterranean region, and Japan (1, 2, 3).

Management

• Avoid ammoniacal nitrogen and maintain soil pH between 6 to 7.
• Rotate with a nonsusceptible crop.
• Sterilize or discard used wooden tomato stakes.
• Plant resistant cultivars.
• Start transplants with disease free seeds and inspect transplants in the greenhouse frequently, roguing any plants that appear weak.
• Fumigate fields as a preventive measure. No fungicides are effective to control this pathogen.
• Do not save seeds from infected fields.
• Till fields in the fall to bury crop residue.
• Consult your local extension specialist for legal and efficacious fungicide products available in your state. Remember, the label is the law and the product applicator is responsible for reading and following all chemical labeling (1, 2, 3).

Diagnostic Procedures

For field diagnositic: See Symptoms and Signs section.

For lab diagnostic: Isolate spores from leaf, stem and roots. This fungus can only be isolated near to the lesion since it does not widely spread into asymptomatic host tissue. Incubate plant material to allow production of spores.

Diagnostic features: It produces three types of spores: macroconidia, microconidia, and chlamydospores. On ½ PDA , it has whitish, fluffy, pale purplish on the top surface. Macroconidia are three to four septate with curved apical cell and a foot-shaped basal cell. Microconidia are unicellular, oval, elliptical, or reinform in shape. (Single spore technique can be found on Bugwoodwiki.)

Culture media:

• ½ PDA with or without antibiotics (streptomycin and ampicillin)
• PDA (Recipe: Distilled water 1L, Potato:200g, Dextrose: 20g, Agar: 20g)
• Fusarium selective media such as Komada’s media is selective for F. oxysporum isolation. However the disadvange is that it can be only good to species level (5).
• Molecular diagnostic methods: PCR (6)

Resources and References

1. Paulus, A.O. 1991. Fusarium Crown and Root Rot, pp. 14. In J.B. Jones, J.P. Jones, R.E. Stall and T.A. Zitter (ed.s), Comendium of tomato diseases. American Phytopathological Society Press, St. Paul, MN.

2. Roberts, P. Disease management: Fusarium crown and root rot on tomato. (http://ipm.ifas.ufl.edu/resources/success_stories/T&PGuide/pdfs/Chapter5/Fusarium.pdf)

3. Zhang, S, P.D. Roberts, R.J. McGovern, and L.E. Datnoff. 2011. Fusarium crown and root rot of tomato in Florida. Pp. 52 (https://edis.ifas.ufl.edu/pg082)

4. Katan, T, D.Zamir, Matti Sarfatti, and J. Katan. 1991.Vegetative Compatibility Groups and Subgroups in Fusarium oxysporum f.sp. radicis-lycopersici. Genetics 81(3): 255-262.

5. Windels, C.E. Fusarium. L.L. Singleton, J.D. Mihail, and C.M.Rush. Methods for research on soilborne phytopathogenic fungi. Pp. 122.

6. http://journals.tubitak.gov.tr/agriculture/issues/tar-13-37-4/tar-37-4-9-1203-71.pdf

Acknowledgments

• National Institute of Food and Agriculture, U.S. Department of Agriculture, under Agreement No. 2011-41530-30708 as part of "Diagnostic Image Series Development for Supporting IPM in the Southern Region" (USDA-NIFA-RIPM-003351)