Streptomyces turgidiscabies

Streptomyces turgidiscabies is a filamentous soil-borne bacterium, a well-known plant pathogen responsible for causing potato scab, including common, net, and deep scab types. It belongs to the genus Streptomyces and is distinguished by its ability to produce thaxtomin toxins, which are critical for the pathogenicity and the development of necrotic lesions on the tubers of susceptible crops.

The primary host for this pathogen is the potato, but it can also infect various root crops such as radishes, carrots, and beets. The infection manifests as shallow or deep pitted lesions on the tuber surface. These scabs significantly degrade the commercial quality of the tubers, making them aesthetically unappealing and reducing their overall market value, while also providing entry points for storage rots.

The biology of Streptomyces turgidiscabies is adapted to the soil environment, where it survives as a saprophyte on decaying plant debris. It colonizes the rhizosphere of developing tubers, typically entering through stomata or lenticels. The infection process is highly dependent on environmental conditions, particularly soil moisture levels and pH, with neutral to alkaline soils significantly increasing the risk of severe outbreaks.

Epidemiological factors facilitating the spread include the planting of infested seed tubers and the movement of contaminated soil via agricultural machinery. Dry soil conditions during the critical tuber initiation stage make the plants particularly susceptible to infection. The pathogen's ability to persist in the soil for several years even in the absence of a host makes it a challenging problem for potato growers worldwide.

Integrated management is essential for controlling this pathogen. Key strategies include:

• Utilizing certified disease-free seed tubers for planting.
• Practicing long-term crop rotation to reduce inoculum density in the soil.
• Adjusting soil pH to acidic levels (below 5.5) where feasible, as the bacterium thrives in neutral and alkaline conditions.
• Ensuring adequate irrigation during the sensitive stages of tuber development to prevent the pathogen from penetrating the lenticels.