Diseases of tomato (
Fusarium crown and root rot
Fusarium crown and root rot of tomato is caused by the fungus Fusarium oxysporum f. sp. radicis-lycopersici. It is a sporadic problem in greenhouses but not in field grown tomatoes in Arizona. Infected plants have a water-soaked appearance at the base, and roots are usually discolored or rotting. Crown and root rot is favored by cool temperatures (10°C to 20°C/50°F to 68°F). Low soil pH, ammoniacal nitrogen, and water-logged soil also exacerbate the disease.
Symptoms appear after green fruit has formed. The first signs are yellowing of the oldest leaves that gradually progresses to the youngest leaves. Plants quickly wilt and die when the disease is severe, but more typically wilting is noted during hot sunny days. The entire root system turns brown and the tap root may rot away. Chocolate brown lesions develop near the soil line and extend up to 10 inches into the vascular system. In contrast, the discoloration extends far up into the plant in Fusarium wilt.
The fungus is found on dead plant material, in the soil and air, on infected plants and on the roots of alternate hosts. It enters through feeder roots and moves through the root system. It may persist for several years.
The most effective way to control this disease is to plant varieties resistant to Fusarium crown and root rot. Infested greenhouses must be completely cleaned and disinfected to manage this disease.
Links to additional information and images:
http://www.ipm.ucdavis.edu/PMG/r783101211.html
http://edis.ifas.ufl.edu/PG082
January 8, 2007