Agrobacterium nepotum

Agrobacterium nepotum is a pathogenic bacterium responsible for bacterial infections in various plant species, primarily affecting the root system and the root collar. As a member of the Rhizobiaceae family, this pathogen alters the hormonal balance of the host plant, forcing the cells to proliferate uncontrollably, which manifests as visible tumors known as galls.

The host range of this bacterium mainly includes fruit-bearing woody plants and various ornamentals. The infection typically occurs through physical wounds on the roots or crown, often sustained during transplanting, pruning, or due to feeding by soil-dwelling insects. Once the bacteria enter the plant tissue, they integrate a portion of their DNA into the host genome, triggering gall formation.

Symptoms are distinct and easy to recognize in advanced stages. Young galls are often light-colored, spongy, and rounded. As the disease progresses, these growths enlarge, become hard, woody, and darker in color. These tumors disrupt the plant's vascular system, leading to stunted growth, reduced nutrient uptake, and overall plant decline, which can result in death if the infection is systemic.

Environmental conditions play a crucial role in the development of Agrobacterium nepotum. The pathogen thrives in moist, well-aerated soils with a neutral to slightly alkaline pH. It can persist in the soil for several years by utilizing decaying organic matter, making it highly difficult to eradicate once it has become established in a particular field or nursery site.

Effective management requires a proactive approach centered on sanitation and prevention. Growers should strictly avoid planting material showing signs of galls. It is essential to practice crop rotation and ensure all tools used in pruning or cultivation are sterilized between uses to prevent the spread of the pathogen. Biological control agents may also be employed to compete with the bacteria in the rhizosphere, effectively reducing the risk of infection.