Paraphoma stem rot

The disease is caused by the fungus Paraphoma chrysanthemicola, a soil-borne pathogen that primarily targets the vascular and root systems of plants. As an opportunistic fungus, it thrives in environments where plants are cultivated in intensive production systems, such as greenhouses or commercial nurseries.

The primary host for this pathogen is the chrysanthemum. It affects various cultivars grown for cut flowers or as pot plants. The fungus colonizes the root zone and the lower stem, disrupting the plant's ability to uptake water and nutrients, which eventually leads to the collapse of the plant.

Initial symptoms are often subtle: leaves begin to yellow, starting from the bottom of the plant. As the infection progresses, the lower foliage wilts and dries out. If the plant is removed from the soil, the root system will show clear signs of necrosis: the roots will appear dark, stunted, and soft compared to the healthy, white roots of unaffected plants.

The development of Paraphoma chrysanthemicola is heavily influenced by high moisture levels and poor soil aeration. The fungus can survive for long periods in infected plant debris or in the soil. It spreads easily through contaminated irrigation water, infested growing media, and the reuse of unsterilized pots or tools.

The economic impact of this disease is significant for the floriculture industry. Once an outbreak occurs in a greenhouse, it can spread rapidly, leading to high mortality rates among the crop. Because it is a root-infecting fungus, it is difficult to treat once symptoms are visible, making preventive measures the most important aspect of management.

• Utilize only pathogen-free cuttings for propagation.
• Steam-sterilize or use fresh, pathogen-free growing media for every crop cycle.
• Implement strict hygiene protocols for tools, benches, and irrigation systems.
• Ensure excellent drainage to prevent prolonged saturation of the root zone.
• Routinely inspect plant root systems for signs of discoloration.