Mollicutes

Mollicutes are a class of specialized bacteria that lack a cell wall and are responsible for numerous systemic diseases in plants, commonly referred to as phytoplasmoses. Unlike other bacteria, they are small and highly specialized, living exclusively within the phloem tissues of their host plants. Their unique biological structure makes them obligate parasites that cannot survive for long periods outside the host or the insect vector.

These pathogens affect a wide variety of economically important crops, including vegetables such as potatoes and tomatoes, fruit trees like peaches and apples, and viticulture crops like grapevines. The infection spreads systematically throughout the vascular system, disrupting the transport of essential metabolites, which eventually leads to the decline and death of the plant.

The clinical signs of infection by Mollicutes are often distinct and easily recognizable by experienced agronomists. Common symptoms include:

• the formation of "witches' brooms" due to excessive branching;
• virescence (greening of flower petals) and phyllody;
• severe chlorosis and leaf rolling;
• stunting and overall failure of fruit and seed development.

Transmission of Mollicutes in fields is strictly dependent on phloem-feeding insect vectors, primarily leafhoppers, psyllids, and aphids. The cycle begins when a vector acquires the pathogen by feeding on an infected plant. After a latent period, the insect becomes a permanent carrier and transmits the pathogen to healthy plants during subsequent feeding sessions. Warm weather conditions significantly accelerate both insect reproduction and pathogen multiplication.

The economic impact of these diseases can be devastating, leading to significant yield losses and total destruction of plantation quality. Management strategies must be preventive, as there is no cure for an infected plant. Effective control involves rigorous weed management to eliminate alternative hosts, the use of insecticides to suppress vector populations, and strict certification of planting materials to ensure they are free from phytoplasmas.