Bacteriophages against Clavibacter michiganensis subsp. michiganensis

Bacteriophages are highly specific viruses that target bacterial cells, functioning as natural antagonists to the plant pathogen Clavibacter michiganensis subsp. michiganensis, which causes tomato bacterial canker.

The mechanism of action involves the adsorption of the phage onto the surface receptors of the target bacteria, followed by the injection of the viral genome into the host cell to initiate the lytic cycle.

This process results in the rapid destruction of the bacterial cell wall and the release of progeny phages, which can then infect neighboring pathogenic cells, maintaining a self-regulating control mechanism.

A major advantage of using bacteriophages is their exquisite specificity, which ensures that beneficial microbes in the soil and on the plant surface remain unharmed throughout the treatment process.

By leveraging these natural lytic agents, growers can effectively reduce the reliance on synthetic chemicals and manage the threat of resistance development in the pathogen population.

The primary target of this biological group is the management of bacterial canker in tomatoes, a devastating disease that affects both greenhouse and open-field production systems globally.

Clavibacter michiganensis subsp. michiganensis causes systemic infections characterized by wilting, vascular necrosis, and the characteristic "bird's eye" spots on the fruit, which render the harvest unmarketable.

Bacteriophages are used to treat seeds to eliminate internal and external inoculum, and are applied to foliage to prevent the spread of the disease during the growing season.

They are particularly valuable in organic farming and integrated pest management (IPM) programs where the use of traditional bactericides and antibiotics is strictly regulated or forbidden.

• Vascular wilting of tomato plants
• Bacterial leaf spot and necrosis
• Fruit infection and spotting
• Transmission via contaminated seeds

Application rates are determined by the titer of the phage preparation (plaque-forming units per ml) and the specific stage of plant development at the time of application.

Seed treatment involves soaking the seeds in a phage solution, which creates an initial line of defense by neutralizing the pathogen before it can colonize the emerging seedling.

Foliar applications are conducted multiple times during the season, with intervals adjusted based on the prevailing weather conditions and the detected levels of infection in the crop.

Applications should ideally be timed for early morning or evening to minimize the negative impact of UV radiation on the viability of the phage particles on the plant surfaces.

When applied through fertigation systems, the concentration must be calculated to ensure that the active biological agents reach the root zone, where the bacteria can persist in crop debris.

The efficacy of bacteriophages is highly dependent on the quality of the water used for mixing; the water should be chlorine-free and maintained at a neutral pH to prevent degradation of the phage particles.

It is strictly prohibited to mix phage products with copper-based pesticides, strong oxidizing agents, or antibiotics, as these will inactivate the biological agents and render the treatment ineffective.

Products must be stored under refrigerated conditions to maintain the stability and titer of the phage; exposure to high temperatures will significantly reduce the shelf life and biological performance.

High temperature and low humidity conditions can lead to rapid evaporation of the spray solution, which may limit the opportunity for phages to locate and infect the target bacterial cells.

Growers should ensure that the phage strains selected are matched to the specific bacterial isolates prevalent in their region to guarantee high levels of disease control.