Fusarium Wilt of Tomato: An Extension Research–Based Overview

Introduction

Fusarium wilt of tomato, caused by the soilborne fungus Fusarium oxysporum f. sp. lycopersici, is one of the most destructive vascular diseases of tomatoes worldwide. Under favorable conditions—warm soils, high humidity, and acidic pH—this pathogen can survive in soil for up to a decade, making management challenging once an area is infested.

Pathogen and Races

F. oxysporum f. sp. lycopersici (Fol) infects tomato roots and colonizes xylem vessels, leading to water and nutrient blockages. Three races of Fol (1, 2, and 3) have been identified, each able to overcome specific resistance genes in tomato cultivars. Race identification is critical: varieties resistant to one race may be susceptible to others.

Host Range

While tomato is the primary host, Fol can infect a broad range of solanaceous and leguminous crops, including potatoes, peppers, eggplants, and various beans. Cross-infection potential underscores the importance of crop rotation and weed management to reduce pathogen reservoirs in the field.

Symptoms and Diagnosis

• Foliar Symptoms: Initial one‐sided wilting of leaves or entire branches, often appearing mid‐season. Lower leaves yellow first, progressing upwards, with permanent wilting regardless of irrigation status.

• Vascular Discoloration: Cutting the stem near the soil line reveals longitudinal brown streaks in the vascular tissue—an unmistakable diagnostic feature.

• Differential Diagnosis: Other wilting agents (Verticillium wilt, bacterial wilt, southern blight, and nematodes) may appear similar, but the distinctive one‐sided yellowing and vascular streaking are characteristic of Fusarium wilt.

Disease Cycle

Fol produces durable chlamydospores that persist in soil or plant debris for years. Under warm (above 60 °F), acidic (pH 5.0 – 5.5), and humid conditions, these spores germinate, infect roots, and move systemically through xylem vessels. Fol sporulation and further chlamydospore production in infected tissues replenish the soil inoculum once plants die or are removed.

Management Strategies

1. Host Resistance

• Resistant Cultivars: Plant varieties carrying the I, I‐2, and I‐3 resistance genes corresponding to races 1, 2, and 3 respectively. Consult the Southeastern U.S. Vegetable Crop Handbook and local extension specialists for race‐specific recommendations.

• Grafting: Use Fusarium‐resistant rootstocks grafted to desired scion varieties; this can extend productivity in high‐pressure fields.

• Crop Rotation: Rotate tomatoes with non‐host crops for 3–5 years. Maintain weed control to prevent alternate hosts (e.g., pigweed, mallow) from sustaining the pathogen.

• Sanitation: Clean equipment and tools between fields to avoid moving infested soil. Use only healthy, symptom‐free transplants and sterile potting mixes when starting seedlings.

• Soil pH Management: Liming to raise soil pH to 6.5–7.0 reduces chlamydospore viability.

• Balanced Nutrition: Avoid excessive ammoniacal nitrogen; favor nitrate‐based fertilizers and maintain adequate potassium to minimize susceptibility.

3. Chemical Control

• Conventional Growers: Soil fumigation can reduce initial inoculum levels. Foliar or drench applications of Miravis® Prime (pydiflumetofen + fludioxonil) provide prophylactic protection when applied before infection occurs.

• Organic Growers: No consistently effective organic fungicides exist; emphasis should remain on resistant varieties and cultural sanitation.

Research Developments

Recent studies highlight the evolutionary arms race between Fol and tomato resistance genes. In California, resistance‐breaking races emerged within 12 years of deploying I‐3–based cultivars, demonstrating the pathogen’s capacity for rapid adaptation. Integrated approaches combining multi‐gene (polygenic) resistance, biological controls (e.g., Trichoderma spp.), and precision soil pH management are under investigation to prolong efficacy of resistance genes and reduce reliance on single‐gene cultivars (PMC).

Conclusions

Fusarium wilt of tomato remains a formidable challenge due to the pathogen’s longevity, race diversity, and capacity for overcoming resistance. A robust management plan integrates resistant cultivars, grafting, crop rotation, soil management, and strict sanitation. Ongoing research into polygenic resistance and biocontrol agents offers promise for sustainable, long‐term control.

References

1. Stokes, C., & Meadows, I. (2021). Fusarium Wilt of Tomato. NC State Extension Publications. NC State Extension

2. Union County Cooperative Extension. (2021). Fusarium Wilt of Tomato. union.ces.ncsu.edu

3. Cai, G. H., McGovern, R. J., & Fisher, N. (2003). Monitoring for a new I3 resistance gene‐breaking race of Fol. Crop Protection, 73, 78–92. PMC