This bacterium affects apples, grapes, peaches, roses, Euonymus and many herbaceous plants. The disease is first seen just above ground level as a swollen, cancer-like structure (often about 5 cm in size) growing out of the stem. It may occasionally cause serious damage, but usually is not a very important problem. The bacterium is able to survive well in soils, and infects the plant through small wounds in the roots.
It is of special scientific interest in the area of plant breeding, having the ability to add its genetic information to that of the plant cell. It does this by means of a small unit of DNA called a 'plasmid'. This plasmid ability of A. tumifasciens has been harnessed by plant breeders to transfer genetic information between unrelated plant species. It is the properties of this bacterium that have led to the new term ' genetically modified crop' or more simply 'GM' (see Chapter 10).
Control of crown gall depends on cultural control methods, such as disease-free propagating material, avoiding wounds at planting time and budding scions to rootstocks (rather than grafting) to avoid injuries near the soil level.
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