Streptomyces

The genus Streptomyces belongs to the kingdom Bacteria and the phylum Actinomycetota. While many species are well-known for producing antibiotics and contributing to soil health, specific phytopathogenic species like Streptomyces scabies are responsible for significant economic losses by infecting various agricultural crops.

The primary disease associated with these pathogens is common scab. This disease mainly affects potato tubers, as well as root crops such as carrots, radishes, and beets. The symptoms manifest as corky lesions, scabs, or deep pits on the surface of the tubers, which significantly reduces the market value and storage potential of the produce.

The biology of these pathogens is characterized by their ability to persist in the soil for long periods as saprophytes on decaying plant organic matter. Infection occurs during the early stages of tuber development when the bacteria enter through lenticels or mechanical wounds. The production of the phytotoxin thaxtomin is the key factor in the development of necrotic lesions.

The spread and severity of the disease are highly dependent on environmental conditions. Streptomyces thrive in light, well-aerated soils with a neutral to slightly alkaline pH (6.0–7.5). Warm temperatures (20–25°C) and dry conditions during the period of tuber initiation provide the most favorable environment for the pathogen to cause extensive damage to the crop.

• Avoid planting susceptible potato varieties in known infested soils.
• Maintain soil moisture at optimal levels during the early tuber bulking stage.
• Use acidifying fertilizers to lower soil pH in susceptible areas.
• Implement proper crop rotation sequences.

Integrated management is essential for controlling Streptomyces, as there are no highly effective chemical cures once the infection is established. Preventive strategies focusing on soil health, irrigation management, and the use of certified, disease-free seed stock remain the most reliable methods for mitigating the impact of common scab.