Bacterial fasciation

Bacterial fasciation is a serious plant disease caused by the gram-positive soil-borne bacterium Rhodococcus fascians. This pathogen is unique because it alters the hormonal balance of the host plant by producing excessive levels of cytokinins, leading to uncontrolled cell division and atypical morphological growth.

The pathogen has a wide host range, primarily affecting popular ornamental plants. Susceptible species include Balsam, Geranium, various Pelargonium species such as Scented-leaf and Ivy-leaf geraniums, as well as several types of Primula, including Primula malacoides, Primula obconica, and Primula vulgaris.

Symptoms are distinct and often referred to as fasciation, where stems and flower stalks become flattened, thickened, and fused together. In severe cases, the plant develops dense clusters of stunted, distorted shoots at the base or crown, often described as a leafy gall or a cauliflower-like growth, which renders the plant stunted and unsalable.

Development and spread are primarily facilitated by contaminated water, infected plant debris, and movement of infested soil. Pathogens are frequently introduced into nurseries via asymptomatic cuttings. High humidity levels and moist conditions on the foliage provide the ideal environment for the bacteria to thrive and colonize new tissue.

Management of this disease is strictly preventative. There is no curative treatment for infected plants; thus, immediate removal and destruction of symptomatic plants are mandatory. Stringent hygiene practices, including regular disinfection of pruning shears and containers, as well as sourcing certified disease-free propagation material, are the only effective ways to control the outbreak.

• Strict quarantine for new nursery stock.
• Immediate removal of symptomatic plants.
• Surface sterilization of all tools.
• Use of sterile propagation media.