Crown gall is a plant disease caused by the soil-borne bacterium Agrobacterium tumefaciens. This bacterium infects a wide range of plants, including many fruit trees, ornamentals, and woody shrubs, and it typically enters the plant through wounds in the roots or stems. Crown gall is characterized by the development of tumor-like growths, known as galls, on the roots, stems, and sometimes branches of infected plants.

Symptoms:

1. Galls: The most characteristic symptom of crown gall is the formation of round, irregularly-shaped galls on the roots, stems, and occasionally branches of infected plants. These galls vary in size and may be smooth or rough in texture, depending on the plant species and strain of the bacterium.
2. Gall color: Galls may initially appear as pale, flesh-colored swellings on plant tissues. Over time, they may darken and become woody or corky in texture as the plant responds to the infection.
3. Reduced growth: Severe infestations of crown gall can lead to reduced growth and vigor in infected plants. Galls disrupt the flow of water and nutrients within the plant, impairing its ability to function and grow normally.
4. Stem or branch dieback: In some cases, crown gall infections can lead to dieback of stems or branches aboveground, especially if galls develop at or near the soil line.

Causes:

Crown gall is caused by the bacterium Agrobacterium tumefaciens, which is naturally present in many soils worldwide. The bacterium enters plant tissues through wounds, such as those caused by transplanting, pruning, or insect feeding. Once inside the plant, Agrobacterium tumefaciens induces the formation of galls by transferring a segment of its DNA, known as a tumor-inducing plasmid, into the plant cells. This DNA segment contains genes that stimulate the plant to produce hormones, causing rapid cell proliferation and the formation of galls.

Recommendations and Preventive Measures:

1. Plant selection: Choose healthy, disease-free plant materials from reputable sources for planting. Avoid planting susceptible species or varieties in areas where crown gall is known to be prevalent.
2. Sanitation: Practice good sanitation in the garden or orchard by removing and destroying infected plant materials, including galls and prunings, to reduce the spread of the bacterium.
3. Avoid wounding: Minimize plant wounds by using sharp, clean pruning tools and avoiding unnecessary pruning or cultivation activities, especially when plants are young or susceptible to infection.
4. Cultural practices: Maintain proper plant nutrition, watering, and soil drainage to promote plant health and vigor. Healthy plants are better able to resist infection and recover from crown gall.
5. Soil sterilization: If crown gall is a recurring problem in a particular area, consider soil sterilization techniques such as solarization or fumigation to reduce the population of Agrobacterium tumefaciens in the soil.
6. Chemical treatments: There are no chemical treatments available to cure crown gall once a plant is infected. However, some chemical compounds, such as gallotannins, have been shown to suppress crown gall development in certain plant species.
7. Genetic resistance: Some plant species or varieties may exhibit genetic resistance or tolerance to crown gall. When possible, select resistant cultivars for planting in areas where crown gall is a concern.

By implementing these preventive measures and practicing good cultural practices, growers can reduce the risk of crown gall infection and minimize its impact on their plants. Early detection, prompt removal of infected plant materials, and integrated pest management strategies are essential components of managing crown gall in gardens, orchards, and landscapes.