crown gall


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crown gall:

see gallgall,
abnormal growth, or hypertrophy, of plant tissue produced by chemical or mechanical (e.g., the rubbing together of two branches) irritants or hormones. Chemical irritants are released by parasitic fungi, bacteria, nematode worms, gall insects, and mites.
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Crown gall

A neoplastic disease of primarily woody plants, although the disease can be reproduced in species representing more than 90 plant families. The disease results from infection of wounds by the free-living soil bacterium Agrobacterium tumefaciens which is commonly associated with the roots of plants.

The first step in the infection process is the site-specific attachment of the bacteria to the plant host. Up to half of the bacteria become attached to host cells after 2 h. At 1 or 2 weeks after infection, swellings and overgrowths take place in tissue surrounding the site of infection, and with time these tissues proliferate into large tumors (see illustration). If infection takes place around the main stem or trunk of woody hosts, continued tumor proliferation will cause girdling and may eventually kill the host. Crown gall is therefore economically important, particularly in nurseries where plant material for commercial use is propagated and disseminated.

Crown gall on peachenlarge picture
Crown gall on peach

Unlike healthy normal cells, crown gall tumor cells do not require an exogenous source of phytohormones (auxins and cytokinin) for growth in culture because they readily synthesize more than sufficient quantities for their own growth. They also synthesize basic amino acids, each conjugated with an organic acid, called opines. The tumor cells also grow about four times faster and are more permeable to metabolities than normal cells.

These cellular alterations, such as the synthesis of opines and phytohormone regulation, result from bacterial genes introduced into host plant cells by A. tumefaciens during infection. Although it is not understood how these genes are introduced into the plant cell, the genes for the utilization of these opines and for regulating phytohormone production have been found to be situated on an extrachromosomal element called the pTi plasmid. This plasmid, harbored in all tumor-causing Agrobacterium species, also carries the necessary genetic information for conferring the tumor-inducing and host-recognition properties of the bacterium.

Crown gall is consequently a result of this unique bacteria-plant interaction, whereby A. tumefaciens genetically engineers its host to produce undifferentiated growth in the form of a large tumor, in which there is the synthesis of a unique food source in the form of an opine for specific use by the bacterial pathogen. See Bacterial genetics, Genetic engineering, Plant hormones, Plant pathology

crown gall

[′krau̇n ‚gȯl]
(plant pathology)
A bacterial disease of many plants induced by Bacterium tumefaciens and marked by abnormal enlargement of the stem near the root crown.
References in periodicals archive ?
Such cold, however, proved Traminette to be susceptible to damage from trunk splitting and some crown gall disease.
radiobacter biovar 2] strain K84 has been used successfully to control crown gall in many plant species.
The crown gall problem casts a dark shadow over vineyards
A list of the approximate dates of key discoveries in the historical record of crown gall disease since about 1900 is shown in Table I.
Smith and Townsend (1907) were among the earlier major investigators of crown gall disease (Braun, 1954, 1982).
1980) examined the effects of several compounds and plant extracts on Crown Gall tumor formation and found no effects on bacterial viability or on the attachment process.
Crown Gall is a neoplastic disease of plants induced by specific strains of A.
If crown gall has appeared in your garden, keep budding knives, grafting tools, and pruning tools clean; sterilize between cuts by dipping them in methyl alcohol or a solution of 1 part sodium hypochlorite (household bleach) to 10 parts water.
While both may test for the presence of crown gall in their foundation blocks, they do not currently certify vine materials for this disease.
Pathogen control: HWT is known to be an effective non-chemical control for a range of pathogens including phytoplasmas and crown gall.
EuroNursery and Vineyards (West) currently offers PCR-based molecular diagnostic testing for Agrobacterium vitis, the crown gall pathogen, and grapevine virus A and B.