Tundu disease of Wheat

Causal Organism and Disease Cycle

Tundu disease is caused by the fungus *Pseudocercospora fici* (formerly *Cercospora fici*). It is an ascomycete fungus that primarily infects fig trees but is highly pathogenic to wheat and barley. The disease cycle is complex and involves several stages:

• Infection: The primary infection occurs through conidia released from infected fig leaves, carried by wind and rain to wheat fields. Conidia enter the plant through stomata or wounds.
• Incubation: After entering the plant, the fungus colonizes the vascular tissues, leading to a latent period.
• Symptom Development: Symptoms begin to appear approximately 2-3 weeks post-infection.
• Conidia Production: The fungus produces abundant conidia within the vascular tissues, which are then released to infect other plants.
• Survival: The fungus survives in infected stubbles and volunteer wheat plants, serving as a primary inoculum source for subsequent seasons.

Symptoms of Tundu Disease

The symptoms of Tundu disease are quite distinctive and progress in a characteristic manner:

• Early Symptoms: Yellowing and chlorosis of the lower leaves, often starting from the tip and margins.
• Vascular Discoloration: Brownish discoloration of the vascular bundles in the stem, visible when the stem is split lengthwise.
• Leaf Drying: Rapid drying and necrosis of leaves, starting from the lower leaves and progressing upwards. The leaves remain attached to the stem for some time.
• Stem Browning: The entire stem becomes brown and brittle.
• Reduced Grain Filling: Affected plants exhibit poor grain filling, resulting in shriveled and lightweight grains.
• Wilting: Severe infections can cause wilting of the entire plant.

Epidemiology and Favorable Conditions

The epidemiology of Tundu disease is influenced by several factors:

• Temperature: Optimal temperature for disease development is between 20-25°C.
• Humidity: High relative humidity (above 80%) favors spore germination and infection.
• Rainfall: Frequent rainfall or irrigation events facilitate spore dispersal and infection.
• Wind: Wind plays a crucial role in disseminating conidia over long distances.
• Proximity to Fig Trees: The presence of infected fig trees in or near wheat fields significantly increases the risk of infection.
• Susceptible Varieties: Certain wheat varieties are more susceptible to Tundu disease than others.

Management Strategies

Managing Tundu disease requires an integrated approach:

• Resistant Varieties: Cultivating wheat varieties resistant to Tundu disease is the most effective control measure.
• Erradication of Fig Trees: Removing infected fig trees within a radius of 500 meters of wheat fields can reduce the inoculum source.
• Crop Rotation: Rotating wheat with non-host crops like rice or legumes can break the disease cycle.
• Seed Treatment: Treating seeds with systemic fungicides can provide early protection against infection.
• Foliar Spray: Applying protective fungicides at early stages of disease development can help control the spread of infection.
• Sanitation: Removing and destroying infected plant debris can reduce the inoculum load.
• Adjusting Sowing Time: Avoiding sowing during periods of high humidity and rainfall can minimize disease incidence.

Geographical Distribution and Economic Impact

Tundu disease is prevalent in East Africa (Uganda, Kenya, Tanzania), parts of Asia (India, Pakistan, Afghanistan), and the Middle East. In India, the disease was first reported in 1968 and has caused significant yield losses in wheat-growing regions like Uttar Pradesh, Punjab, and Haryana. The economic impact is substantial, with yield losses ranging from 20% to 80% depending on the severity of the infection and the susceptibility of the variety.