Spiroplasma

Spiroplasma is a genus of plant pathogenic bacteria belonging to the class Mollicutes. These microorganisms lack a cell wall, which makes them highly adaptable to various environmental stresses. They primarily colonize the phloem tissue of plants, where they function as systemic parasites, disrupting the flow of essential nutrients and leading to the eventual decline of the host plant.

Various crops can be affected by these pathogens, most notably corn (Spiroplasma kunkelii) and citrus (Spiroplasma citri). The infection disrupts the source-to-sink transport of photoassimilates, which is critical for plant development. Because these pathogens rely on the phloem for nutrients and transport, they effectively colonize the entire vascular system of the host shortly after initial infection.

Symptoms of Spiroplasma infection are diverse but generally include yellowing of the leaves, stunted plant growth, and a reduction in fruit or grain size. In many cases, infected plants exhibit a bushy appearance due to shortened internodes and excessive lateral growth. Severe chlorosis, leaf reddening, and significant yield losses are standard indicators of an advanced stage of the disease.

The transmission of Spiroplasma is entirely dependent on sap-sucking insect vectors, primarily leafhoppers. The pathogen undergoes a latent period within the insect body before it can be transmitted to a healthy plant. The spread of the disease is strictly correlated with the migration patterns and population density of these vectors, making environmental and weather conditions critical factors for the epidemic scale of the disease.

Effective management strategies focus on preventing the spread of the disease rather than curative treatments, as there are no direct chemical controls for the pathogen itself. Management includes:

• monitoring and controlling insect vector populations with systemic insecticides;
• removing infected plants and alternative weed hosts from the field;
• using certified disease-free propagation material;
• implementing quarantine measures to prevent the spread to non-infested regions;
• selecting resistant or tolerant crop varieties.