Crown Gall Disease

Behavior

''A. tumefaciens'' is an alphaproteobacterium of the family Rhizobiaceae, which includes the nitrogen-fixing legume symbionts. Unlike the nitrogen-fixing symbionts, tumor-producing ''Agrobacterium'' species are pathogenic and do not benefit the plant. The wide variety of plants affected by ''Agrobacterium'' makes it of great concern to the agriculture industry.

Economically, ''A. tumefaciens'' is a serious pathogen of walnuts, grape vines, stone fruits, nut trees, sugar beets, horse radish, and rhubarb, and the persistent nature of the tumors or galls caused by the disease make it particularly harmful for perennial crops.

''A. tumefaciens'' grows optimally at 28 °C. The doubling time can range from 2.5–4h depending on the media, culture format, and level of aeration. At temperatures above 30 °C, ''A. tumefaciens'' begins to experience heat shock which is likely to result in errors in cell division.

Habitat

Host, environment, and pathogen are extremely important concepts in regards to plant pathology. ''Agrobacteria'' have the widest host range of any plant pathogen, so the main factor to take into consideration in the case of crown gall is environment. There are various conditions and factors that make for a conducive environment for ''A. tumefaciens'' when infecting its various hosts.

The bacterium can't penetrate the host plant without an entry point such as a wound. Factors leading to wounds in plants include cultural practices, grafting, freezing injury, growth cracks, soil insects, and other animals in the environment causing damage to the plant. Consequently, in exceptionally harsh winters, it is common to have an increased incidence of crown gall due to the weather-related damage. Along with this, there are methods of mediating infection of the host plant. For example, nematodes can act as a vector to introduce ''Agrobacterium'' into plant roots. More specifically, the root parasitic nematodes damage the plant cell, creating a wound for the bacteria to enter through. Finally, temperature is a factor when considering ''A. tumefaciens'' infection. The optimal temperature for crown gall formation due to this bacterium is 22 degrees Celsius because of the thermosensitivity of T-DNA transfer. Tumor formation is significantly reduced at higher temperature conditions.