Actinomycosis of plants

Causative agent and disease type. Actinomycosis of plants is a condition caused by members of the Actinomycetales order, a group of Gram-positive, filamentous bacteria. These organisms, often referred to as actinomycetes, are primarily soil-dwelling saprophytes. However, certain species, such as Streptomyces scabies, act as opportunistic pathogens that invade the subterranean parts of plants, causing distinct necrotic lesions commonly known as common scab.

Affected crops. This disease mainly targets root and tuber crops, significantly impacting their commercial value. The most frequently affected species include potatoes, sugar beets, carrots, radishes, and parsnips. The bacteria inhabit the soil environment and attack the plants by penetrating the periderm of the developing tubers or taproots, utilizing natural lenticels or small mechanical wounds as entry points.

Symptoms and signs. The visual indicators of the disease are characterized by surface lesions. Depending on the level of infection and plant reaction, these may appear as superficial scabs, pitted deep lesions, or raised, corky malformations. In severe cases, the infected area covers a significant portion of the vegetable surface, causing desiccation of tissues and making the produce unappealing for the market and susceptible to subsequent storage rot.

Conditions for development. The activity and virulence of actinomycetes are strongly influenced by the environmental conditions of the soil. They thrive in loose, aerated soils with a neutral or slightly alkaline pH (6.0–7.5). Dry conditions during the early stages of tuber formation are particularly conducive to the disease, as low moisture levels prevent the plant from effectively warding off the bacterial colonization of its skin.

Protective measures. Integrated management is essential for controlling actinomycetes in the field. Key strategies include practicing long-term crop rotation to reduce bacterial density in the soil, utilizing physiological acidifying fertilizers, and ensuring consistent moisture levels during critical growth phases. Furthermore, selecting resistant cultivars and incorporating biological control agents can significantly lower the incidence of the disease in commercial agricultural production.