Celery phoma rot

The fungus survives in soil, infected plant debris, and can be transmitted via infested celery seeds. The mycelium remains dormant in seeds, making them a primary vector for spreading the disease to new planting sites.

The pathogen reproduces by forming small black fruiting bodies called pycnidia, which produce numerous spores. These spores are released under humid conditions and are disseminated by wind, rain splashes, and irrigation water.

The infection cycle begins when spores land on plant tissue, germinate, and penetrate the epidermis. The fungus then colonizes the internal tissues, leading to cell death and the formation of characteristic lesions.

This pathogen is highly adapted to the host, allowing it to complete its life cycle efficiently under favourable climatic conditions, especially in regions with consistent rainfall or high humidity.

Early symptoms of phoma rot in celery include the appearance of small brown or greyish spots on the leaves and petioles. These spots gradually expand, turning into necrotic, dry lesions.

On roots and tubers, the disease manifests as sunken, dark-brown spots. A diagnostic feature is the presence of tiny, black, pimple-like structures — the pycnidia — scattered across the affected surface.

As the infection progresses, the lower part of the petioles and the crown of the root may become blackened and brittle, causing the leaves to yellow, wilt, and collapse, eventually leading to plant death.

When an infected root is cut open, one often finds dry, brown internal decay. Unlike bacterial soft rots, the tissue remains relatively firm but becomes discoloured, spongy, and necrotic.

In cases of high humidity, a thin, grayish fungal mat may occasionally appear on the surface of the lesions, particularly around the collar region of the plant.

High humidity and moisture are the most critical factors for the development and spread of Calophoma complanata. Rain-fed agriculture and overhead irrigation systems significantly favor the germination of spores.

The optimal temperature range for the rapid development of the pathogen is between +18°C and +25°C. During warm, humid summers, the disease can spread rapidly through a field if proper hygiene is neglected.

Dense planting patterns reduce air circulation, maintaining a humid microclimate around the plant base that is highly conducive to fungal infection and the rapid expansion of necrotic lesions.

Failure to rotate crops allows the fungus to accumulate in the soil, significantly increasing the risk of infection in subsequent planting seasons, as the pathogen can persist in the soil for several years.

Poor soil drainage creates an environment that stresses the plant and facilitates the movement of pathogens. Plants under stress show reduced natural resistance, allowing the fungus to penetrate and establish more easily.

The economic impact of phoma rot is severe, as the disease can persist and continue to develop during storage, rendering affected batches of celery unmarketable or even entirely useless.

Reduction in the leaf surface area due to necrotic spots impairs photosynthesis, which negatively affects the growth and size of the root, leading to lower yields and inferior quality of the harvest.

Seedling blight caused by the pathogen can result in major plant stand losses, necessitating expensive replanting and disrupting the production schedule for commercial growers.

The quality of the product is greatly compromised; the dry rot lesions make the vegetable unsightly and can ruin the flavor profile, making the crop unsuitable for sale in fresh produce markets.

Farmers face significant losses due to the need for post-harvest sorting, where infected roots must be discarded, further increasing labor costs and reducing overall profitability.

Effective management requires starting with disease-free, high-quality seeds. Treating seeds with authorized fungicides is a critical step in preventing the introduction of the pathogen to clean fields.

Implementing a strict crop rotation program (at least 3-4 years without host crops like celery or parsley) is essential to reduce the inoculum levels in the soil naturally.

Proper field sanitation, including the removal and deep burying or burning of infected plant debris after harvest, helps minimize the overwintering potential of the fungus.

If the disease appears in the field, targeted applications of systemic fungicides can help control the spread. It is important to alternate chemical classes to prevent the development of resistant fungal strains.

• Use drip irrigation to keep foliage dry.
• Ensure adequate spacing between plants for airflow.
• Monitor crops regularly for the first signs of symptoms.
• Sanitize storage facilities thoroughly before harvest.