Hibiscus greening phytoplasma

Systematic position and pathogen type. Hibiscus greening phytoplasma belongs to the class Mollicutes, specifically to the group of specialized phytoplasmas. These organisms lack a rigid cell wall and are obligate parasites living exclusively within the plant phloem tissue. They are known for causing severe developmental abnormalities in ornamental plants, specifically impacting the hormonal balance related to flowering.

Diseases and susceptible hosts. The primary host is the Chinese hibiscus (Hibiscus rosa-sinensis). The characteristic symptom is virescence, where the petals turn green, resembling leaves. This is often accompanied by phyllody, where floral organs are transformed into leafy structures, and abnormal proliferation of shoots known as witch's broom, significantly altering the plant's aesthetic value.

Biology and life cycle. The pathogen is transmitted by phloem-feeding insects, primarily leafhoppers. The transmission process is persistent: the insect acquires the phytoplasma by feeding on an infected plant, the pathogen multiplies within the insect's salivary glands, and is later injected into healthy plants. The latency period within the host can be extensive, making early diagnosis difficult.

Conditions of spread and economic impact. The spread of the disease is highly correlated with the movement and population density of insect vectors. It thrives in warm climates where insect activity is year-round. Economically, this is a devastating disease for the ornamental nursery industry, as infected plants are generally unsalable and provide a continuous source of inoculum for neighboring plants.

Protection and control measures. Management of phytoplasma diseases is difficult due to the lack of curative treatments. The following strategies are essential for effective control:

• Strict sanitation by removing and destroying symptomatic plants immediately.
• Integrated pest management (IPM) to control leafhopper and other vector populations.
• Using only certified, disease-free cuttings for propagation.
• Maintaining a clean environment around greenhouses to eliminate alternative hosts for the pathogen.