Tomato big bud phytoplasma

Systematic position and type of pathogen. Tomato big bud is caused by a phytoplasma, a specialized type of bacteria belonging to the class Mollicutes. Lacking a rigid cell wall, these microscopic pathogens inhabit the phloem tissue of host plants. They are obligate parasites that rely on phloem-feeding insects to move from one plant host to another.

Diseases and host crops. The pathogen causes a systemic disease commonly referred to as "big bud" due to the characteristic enlargement of flower buds. The primary hosts include tomatoes, but the disease also affects various other solanaceous crops such as peppers, eggplants, and potatoes. Furthermore, many wild weed species act as symptomless or latent reservoirs for the pathogen.

Biology and life cycle. Transmission occurs through the feeding activity of phloem-sucking insects, particularly leafhoppers. When a leafhopper feeds on an infected plant, it ingests the phytoplasma. After a latent period during which the pathogen multiplies within the insect, the vector becomes capable of transmitting the disease to healthy plants during subsequent feeding sessions.

Development and severity. Development is favored by hot and dry environmental conditions that promote the movement and population growth of insect vectors. The symptoms include extreme deformation of floral parts, leaf yellowing, stunting, and bushy growth. In tomatoes, the fruit becomes small, woody, and deformed, resulting in total yield loss in severely affected patches.

Control and management measures. Managing the disease is focused on breaking the cycle of insect transmission and eliminating reservoir hosts. Effective control strategies include:

• Managing weeds in and around fields to remove inoculum sources.
• Monitoring and controlling leafhopper populations using appropriate insecticides.
• Using protective screens in greenhouse environments to exclude vectors.
• Choosing resistant or tolerant cultivars when available.
• Roguing and destroying plants showing early symptoms to prevent further spread.