Pectobacterium zantedeschiae

The causative agent of this disease is the bacterium Pectobacterium zantedeschiae, a gram-negative plant pathogen. It is highly specialized in infecting plants within the Araceae family. The bacterium acts by secreting cell wall-degrading enzymes that break down the plant structure, leading to systemic tissue collapse.

The primary hosts for this pathogen are Zantedeschia species, commonly known as Calla lilies. The disease affects both greenhouse and outdoor plantings, often introduced through contaminated tubers or infested irrigation water. Once inside the host, the bacteria rapidly colonize the vascular and parenchymal tissues.

Symptoms include water-soaked lesions appearing on petioles and stalks, which quickly turn into soft, mushy, and malodorous rot. The foliage wilts unexpectedly, and the subterranean parts, such as rhizomes and tubers, become dark and necrotic. The entire plant structure may collapse within a few days under favorable conditions.

Development and spread are triggered by high humidity, poor soil drainage, and warm temperatures, typically ranging from 20°C to 28°C. The pathogen can persist in soil debris or on infected tubers, making it difficult to eradicate once a greenhouse or field site is heavily contaminated.

Management strategies require a comprehensive approach to hygiene and cultural practice:

• Strict culling of any plant material showing signs of rot during the dormancy phase.
• Improving soil aeration and avoiding overhead irrigation to keep foliage dry.
• Sterilizing all horticultural tools with effective disinfectants between plants.
• Applying biological control agents, specifically beneficial bacterial strains, to the root zone.
• Ensuring proper post-harvest drying and storage conditions for dormant tubers to inhibit bacterial growth.