Streptomyces scab

Streptomyces scab is a bacterial disease caused by Streptomyces netropsis, a type of filamentous soil bacteria. These pathogens are ubiquitous in agricultural soils and can persist in organic matter for many years, making them difficult to eradicate once the soil is infested.

The disease primarily affects root and tuber crops, with potatoes being the most susceptible host. The infection typically occurs during the early stages of tuber or root development, as the bacteria enter the plant tissue through lenticels or small wounds in the skin.

The diagnostic symptoms include the development of superficial, raised, or pitted lesions on the tubers' surface. These lesions are typically corky in texture, often described as scabs, which negatively impact the aesthetic quality of the harvest and decrease market value significantly.

Development of the disease is highly favored by specific environmental conditions. Streptomyces netropsis thrives in alkaline or neutral soils with a pH level above 6.5 and is most aggressive when soil moisture levels are low during the critical tuber initiation stage. Poorly managed irrigation can drastically worsen the severity of the scab.

In terms of agricultural impact, the disease leads to significant storage losses. The compromised skin of infected tubers provides easy access for soft rot bacteria and other opportunistic fungi, leading to rot in storage. Effective management strategies focus on modifying soil conditions and implementing robust crop rotation practices.

• Implementing crop rotation with non-host plants or green manures.
• Maintaining soil pH at slightly acidic levels to discourage pathogen growth.
• Ensuring adequate soil moisture during the tuber initiation period.
• Using certified, disease-free seed tubers for planting.
• Avoiding the application of fresh manure just before planting seasons.