Celery Phoma rot

The first symptoms of Phoma rot often appear on leaves and petioles as yellow or brown spots, which eventually show tiny dark pycnidia.

On roots, the disease manifests during harvest or storage as dry, sunken, grayish or brownish rot patches that penetrate deep into the flesh.

Internal tissues of the root become pithy and may develop cavities filled with fungal mycelium, often appearing white or light gray.

A distinct boundary is usually visible between healthy and infected tissues, which helps in identifying the disease during inspection.

In advanced stages, the infected area of the root surface becomes depressed, causing the plant to lose structural integrity and quality.

The pathogen is the fungus Subplenodomus apiicola, formerly known as Phoma apiicola, a specialized agent targeting celery.

The fungus survives as pycnidia on crop debris in the soil and can also be seed-borne, allowing for early season infections.

Spore dispersal occurs via wind, splashing rain, irrigation water, and contaminated tools used during field cultivation.

This fungus is highly adaptive and can persist as a saprophyte in the soil for several years in the absence of a host crop.

Genetic diversity of the pathogen allows it to overcome minor physiological barriers of the host, leading to successful colonization of celery roots.

Cool and wet weather conditions, particularly late in the growing season, are highly conducive to the development and spread of Phoma rot.

Optimal temperatures for mycelial growth and spore production range between 15°C and 20°C, typical of early autumn weather.

Poor field management, including overcrowding of plants, leads to stagnant air and high humidity, which significantly accelerates disease progress.

Frequent rainfall keeps the canopy moist, facilitating the germination of spores on foliage and subsequent downward transport to the roots.

In storage facilities, high humidity (above 85%) combined with inadequate airflow creates the perfect environment for the rot to spread between roots.

The primary damage includes significant post-harvest losses, as infected roots deteriorate rapidly in storage, contaminating surrounding healthy produce.

Marketable yield is severely reduced due to the cosmetic damage and internal degradation of the celery roots, making them unsellable.

Infected crops show stunted growth and reduced biomass, leading to lower overall weight and lower economic return for the farmer.

Seed-borne transmission can lead to poor stand establishment, necessitating replanting and increasing production costs.

Secondary infections often take advantage of tissues weakened by Subplenodomus apiicola, further compounding the degradation of the harvest.

The most effective strategy involves using certified disease-free seeds and performing professional seed treatment to eliminate potential pathogens.

A robust crop rotation program, excluding celery and related apiaceous plants for at least four years, is essential to starve the fungus.

• Prompt removal and destruction of crop residues post-harvest to reduce the inoculum level.
• Deep plowing to bury infested plant debris and accelerate biological decomposition.
• Strict monitoring of moisture and ventilation in storage environments.
• Avoiding excessive nitrogen fertilization that leads to succulent, susceptible tissue growth.
• Careful harvesting to prevent wounding roots, which act as entry points for the fungus.

Fungicide applications during the vegetative phase can suppress initial outbreaks, especially in high-risk, wet weather conditions.

Sorting and grading harvested produce to remove symptomatic roots before long-term storage is critical to protecting the stored inventory.