Raspberry crown gall

Agrobacterium rubi is a gram-negative soil bacterium belonging to the genus Agrobacterium. It serves as a significant phytopathogen responsible for causing crown gall disease in various rosaceous plants, with a primary focus on blackberries and raspberries.

The infection manifests as tumor-like growths, known as galls, which form on the roots and the crown of the plants. These galls are caused by the genetic transformation of plant cells, where the bacterium inserts its T-DNA into the host genome, forcing the plant to overproduce growth hormones and nutrients that support the bacterium's survival.

The lifecycle of Agrobacterium rubi involves surviving in the soil and infecting plants through wound sites caused by insect feeding, pruning, or cultivation activities. Once inside, the bacterium triggers uncontrolled cell division in the host tissue, leading to the formation of the characteristic gall structures that disrupt the plant's vascular system.

Environmental conditions such as high soil moisture and moderate temperatures are ideal for the survival and spread of the pathogen. Soils with neutral to slightly alkaline pH are generally more conducive to disease development. Because the bacterium remains viable in the soil for years, it poses a long-term threat to orchard productivity.

The economic impact of the disease is severe, as it prevents the efficient uptake of water and minerals, leading to stunting, poor yields, and sometimes plant death. Key indicators of infestation include:

• Development of spongy or hard, irregular galls on roots and stems.
• Reduced vigor and stunted canopy growth.
• Yellowing of foliage and poor fruit development.
• Increased susceptibility to winter injury and abiotic stress.

Control strategies rely heavily on sanitation and prevention. Growers should strictly use certified disease-free nursery stock, as the primary spread occurs through infected plant material. Implementing long crop rotations and avoiding planting in infested soil are critical. Furthermore, protecting roots from mechanical injury during fieldwork is essential to minimize entry points for the bacteria.