Oidium lycopersicum

Fungal Disease

Oidium lycopersicum

Fungal Disease

Oidium lycopersicum

Fungal Disease

Powdery Mildew of Tomato: A Growing Concern

Powdery mildew of tomato has become a significant disease problem worldwide, affecting both field and greenhouse production. Since the early 1990s, outbreaks have been reported in Europe, North and South America, and Asia. This disease primarily impacts leaves, leading to yellowing, necrosis, and defoliation, ultimately reducing fruit production by up to 50% in severely affected regions.

Symptoms and Diagnosis

• Can infect tomato plants at any growth stage under favorable conditions.
• Early symptoms include light green and yellow blotches on leaves.
• White, powdery fungal growth with dense sporulation appears on the upper leaf surface.
• Chlorotic lesions turn purple with necrotic centers as the infection progresses.
• High humidity and cloudy conditions may lead to mildew formation on the underside of leaves.
• Severe infections cause leaf distortion, while petioles and stems may also be affected.
• Fruits remain uninfected.

Disease Development and Spread

• Caused by Oidium neolycopersici, an obligate fungal parasite.
• Affects solanaceous crops like pepper, eggplant, potato, and tobacco.
• Fungus survives in living or dormant host plants.
• Spreads via airborne conidia, which can travel long distances.
• Infection cycle repeats multiple times during the growing season.

Environmental Factors Influencing Disease Progression

• Temperature:
  • Optimal disease development occurs at 20–25°C.
  • High temperatures (30°C+) inhibit spore germination and disease spread.
  • Short exposures (2–3 hours daily) to 35°C can suppress the disease by 70–92%.
• Humidity:
  • Low RH (20–40%) reduces spore germination but accelerates host tissue death.
  • Intermediate RH (50–70%) promotes disease development.
  • High RH (80–90%) favors spore germination but restricts lesion growth.

Conclusion

Powdery mildew remains a critical threat to tomato production, significantly impacting yield and plant health. Understanding its symptoms, spread, and environmental influences is essential for effective management in commercial tomato-growing regions.