''Allorhizobium vitis'' is a plant pathogen that infects

grapevines ''Vitis'' (grapevine) is a genus of 79 accepted species of vining plants in the flowering plant family Vitaceae. The genus is made up of species predominantly from the Northern Hemisphere. It is economically important as the source of grapes, b ...

. The species is best known for causing a

tumor A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...

known as crown gall disease. One of the virulent strains, ''A. vitis'' S4, is responsible both for crown gall on grapevines and for inducing a

hypersensitive response Hypersensitive response (HR) is a mechanism used by plants to prevent the spread of infection by microbial pathogens. HR is characterized by the rapid death of cells in the local region surrounding an infection and it serves to restrict the growt ...

in other plant species. Grapevines that have been affected by crown gall disease produce fewer grapes than unaffected plants. Though not all strains of ''A. vitis'' are tumorigenic, most strains can damage plant hosts. ''A. vitis'' shares many genetic and morphological characteristics with several ''Agrobacterium'' species, including ''A. tumefaciens''. The two species have overlapping host ranges, and both ''A. vitis'' and ''A. tumefaciens'' may reduce the yield of infected crops. For this reason, research on ''A. vitis'' focuses on transmission and methods of control.

Biology

Identification

''A. vitis'' is a

Gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall ...

bacterium with a thin peptidoglycan layer in its

cell wall A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mech ...

. The species is aerobic and

mesophilic A mesophile is an organism that grows best in moderate temperature, neither too hot nor too cold, with an optimum growth range from . The optimum growth temperature for these organisms is 37°C. The term is mainly applied to microorganisms. Organi ...

, with individual cells that are

rod-shaped A bacillus (), also called a bacilliform bacterium or often just a rod (when the context makes the sense clear), is a rod-shaped bacterium or archaeon. Bacilli are found in many different taxonomic groups of bacteria. However, the name ''Bacillu ...

and motile. On culture, colonies are round, white, and translucent.

Range and environment

The presence of ''A. vitis'' has been confirmed in Germany, France, Austria, Hungary, South Africa, and the United States. Crown gall disease outbreaks in Europe and North America in the mid-1980s have been linked to ''A. vitis'', and the species has continued to survive in those regions. Additionally, a survey conducted in China from 2003 to 2009 identified strains of ''A. vitis'' on

blight Blight refers to a specific symptom affecting plants in response to infection by a pathogenic organism. Description Blight is a rapid and complete chlorosis, browning, then death of plant tissues such as leaves, branches, twigs, or floral organ ...

ed banana plants.

Genetic traits

Chromosome and plasmids

The genome of ''A. vitis'' consists of two circular chromosomes and five plasmids. It is 6.32 Mb long and encodes 5549 proteins. Four rRNA operons have been identified. Tumorigenic strains contain a Ti plasmid (pTi). Ti plasmids in galls produce various opines that are then secreted from the gall. In a vitis, pTi codes for octopine and/or cucumopine. Tumorigenic strains also contain a plasmid that allows the bacterium to utilize tartrate.

Classification

''A. vitis'' was formerly referred to as ''

Agrobacterium ''Agrobacterium'' is a genus of Gram-negative bacteria established by H. J. Conn that uses horizontal gene transfer to cause tumors in plants. ''Agrobacterium tumefaciens'' is the most commonly studied species in this genus. ''Agrobacterium'' is ...

biovar A biovar is a variant prokaryotic strain that differs physiologically or biochemically from other strains in a particular species. Morphovars (or morphotypes) are those strains that differ morphologically. Serovars (or serotypes) are those strain ...

III. Originally, the species included only biovar III strains found in grape hosts. Since then, ''A. vitis'' has been redefined to include all biovar III strains. It can be distinguished from biovars I and II, ''A. tumefaciens'' and '' A. rhizogenes'', on the basis of its hosts and pathogenicity. Fatty acid analysis also reveals differences between ''A. vitis'' and other strains of tumorigenic bacteria. ''A. vitis'' has also been classified in the genus ''

Rhizobium ''Rhizobium'' is a genus of Gram-negative soil bacteria that fix nitrogen. ''Rhizobium'' species form an endosymbiotic nitrogen-fixing association with roots of (primarily) legumes and other flowering plants. The bacteria colonize plant cells ...

''. A 1999 study suggested that ''A. vitis'' is more closely related to ''

Rhizobium galegae ''Neorhizobium galegae'' is a Gram negative root nodule bacteria. It forms nitrogen-fixing Nitrogen fixation is a chemical process by which molecular nitrogen (), with a strong triple covalent bond, in the air is converted into ammonia () or r ...

'' than to other ''Agrobacterium'' species, based on genetic sequence comparison. In 2001, Young ''et al.'' proposed that ''A. vitis'' be reclassified as ''Rhizobium vitis''. More recently, ''A. vitis'' was transferred to the genus ''

Allorhizobium ''Allorhizobium'' is a genus of Gram-negative soil bacteria. Some species of ''Allorhizobium'' form an endosymbiotic nitrogen-fixing association with roots of legumes A legume () is a plant in the family Fabaceae (or Leguminosae), or the f ...

''.

Pathogenicity

Hosts

Grapevines are the plants most commonly infected with ''A. vitis''. Though ''A. vitis'' may cause hypersensitive response in other plant species, crown gall disease induced by tumorigenic ''A. vitis'' is unique to grapevines. All strains of ''A. vitis'' induce grape root

necrosis Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. Necrosis is caused by factors external to the cell or tissue, such as infection, or trauma which result in the unregulated dige ...

. Because ''A. vitis'' may remain latent, not all infected plants show symptoms. An intraspecific taxon of ''A. vitis'' has been isolated from banana leaves in China. ''A. vitis'' may also infect tomato plants, and has been shown to cause leaf panel collapse in

tobacco Tobacco is the common name of several plants in the genus '' Nicotiana'' of the family Solanaceae, and the general term for any product prepared from the cured leaves of these plants. More than 70 species of tobacco are known, but the ...

Transmission

The

Ti plasmid A tumour inducing (Ti) plasmid is a plasmid found in pathogenic species of ''Agrobacterium'', including ''A. tumefaciens, ''A. rhizogenes'', ''A. rubi'' and ''A. vitis''. Evolutionarily, the Ti plasmid is part of a family of plasmids carried b ...

is responsible for transmission of crown gall disease in plants infected with ''A. vitis''. Tumorigenic ''A. vitis'' transfers its Ti plasmid to other bacteria, and transfers

T-DNA The transfer DNA (abbreviated T-DNA) is the transferred DNA of the tumor-inducing (Ti) plasmid of some species of bacteria such as ''Agrobacterium tumefaciens'' and ''Agrobacterium rhizogenes(actually an Ri plasmid)''. The T-DNA is transferred fr ...

into plants. Virulence genes encoded by the Ti plasmid generate single-strand T-DNA molecules, which in turn are transferred to healthy hosts. Disorganized cell division occurs in infected hosts, leading to gall development instead of the formation of healthy vascular tissue. Propagation of diseased wood often transmits ''A. vitis''. Injuries to a grapevine caused by cutting or freezing may also make the plant more susceptible to crown gall infection. However, galls grow only on trunks or canes, and do not appear on the roots of infected plants.

In Agriculture

Crown gall disease

When ''A. vitis'' causes crown gall disease, several symptoms and tests can be used to identify its presence. On grapevines, young galls appear as soft green bumps, which later become brown and rough. Galls do not appear on all grapevines in which ''A. vitis'' is present. Steps can be taken to control crown gall disease and reduce the risk of infection. Injured sites on vines, such as those caused by freezing or cutting injuries, are especially susceptible to infection. Planting in frost-prone areas or areas with poor drainage should therefore be avoided. Reducing other grapevine stressors, such as nutrient deprivation and low soil pH, also limits susceptibility. Additionally, some

cultivar A cultivar is a type of cultivated plant that people have selected for desired traits and when propagated retain those traits. Methods used to propagate cultivars include: division, root and stem cuttings, offsets, grafting, tissue culture, ...

s are resistant to crown gall disease. ''

Vitis vinifera ''Vitis vinifera'', the common grape vine, is a species of flowering plant, native to the Mediterranean region, Central Europe, and southwestern Asia, from Morocco and Portugal north to southern Germany and east to northern Iran. There are curre ...

'' is generally susceptible to crown gall disease, but resistant grape species can be planted preferentially.

Other diseases

Grape necrosis is a common symptom of ''A. vitis'' infection, caused by both tumorigenic and non-tumorigenic bacteria strains. Tobacco leaf panel collapse can be induced by the non-tumorigenic F2/5 strain of ''A. vitis''. While the strain of ''A. vitis'' found in grapevines, ''A. vitis pv. vitis'', is responsible for most diseases, banana leaf blights have been linked to ''A. vitis pv. musae''.

Nonpathogenic strains

Strains of bacteria can be used as biological control agents to limit the growth of pathogenic ''A. vitis''. Grapevine roots that have been soaked in a suspension containing the inhibitory strain are less susceptible than those that have not. Several ACC deaminase-producing species found in the rhizosphere inhibit ''A. vitis'' tumor production in tomato plants. Non-tumorigenic strains of ''A. vitis'' (F2/5, ARK-1, and VAR03-1) have been shown to limit crown gall formation. In investigations involving these strains, F2/5 still induced necrosis but ARK-1 did not.

References

External links

Type strain of ''Allorhizobium vitis'' at Bac''Dive'' - the Bacterial Diversity Metadatabase