Rhizobium [Agrobacterium] radiobacter (previously known as A. tumefaciens) is an aerobic, gram-negative, motile, rod-shaped bacterium ...

Symptoms of plants infected with Rhizobium radiobacter are dependent on the type of host infected.

The first symptom plants commonly exhibit when infected by Rhizobium radiobacter is the presence of tumorous overgrowths (galls) on the roots, stem (trunk), and crown at or below the soil surface. Initially, these galls are round, white or flesh colored, and soft and spongy. In later stages, the emerging gall develops into a woody interior with an irregular, rough, corky surface. This outer tissue darkens. The gall color will range from light brown to black depending on age and host. Size also varies ranging from 5 to 16 cm diameter. In trees, galls can sometimes grow to be 30 cm diameter. As galls age, the outer surface may slough off and crack due to normal rotting, weathering, and secondary microorganism activity leading to further tissue breakdown. However, galls can reappear in the same places the following year along with the formation of new tissues. Some host plants develop secondary tumors at a few inches above or below the previous site of infection. Severely infected plants lack vigor, have stunted leaves, may turn yellow or red, and shoots often die back. Wilting and death are the primary symptoms of continued infection. Death is more common when galls occur at the plant's base and girdle the stem of the host, blocking the vascular system. Young plants are more susceptible to the disease and are also more likely to die from the disease ...

Rhizobium radiobacter is a soilborne pathogen that can survive in the soil or inside plants as a parasite. There are over 600 plant species and over 90 plant families that are susceptible to crown gall ... Infection of Rhizobium radiobacter is most likely to occur under the following conditions: 1) temperatures above 20°C; 2) during times of high humidity; and 3) when the host surfaces are moist due to rainfall. The pathogen can be spread through rain, irrigation water, wind, insects, tools, and use of contaminated soil during propagation or planting. Detached galls that rest on the ground or in the soil are primary inoculum sources ...

- John Bonkowski, Bacheline Joseph, and Deanna Bayo: (updated 2014) Agrobacterium tumefaciens^©