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Crown gall is a plant disease caused by Agrobacterium tumefaciens, a soil-dwelling bacterium. The bacterium induces irregular growths or galls on the roots, twigs, and branches of euonymus and other rose-related shrubs.
The bacterium causes the galls by stimulating the rapid growth of plant cells. The galls weaken and stunt the plant's growth, in addition to being unsightly. Despite the fact that galls can obstruct the flow of water and nutrients up the roots and branches, they seldom result in the death of the plant. Via polluted soil and equipment, the disease will spread to other plants. The majority of chemical therapies are ineffective.
Phomopsis sp. is thought to be the cause of galls on forsythia, viburnum, highbush blueberry, American elm, hickory, maple, oak, and privet. Since the cultural controls for bacterial crown gall are the same, both are viewed together here. Chemical therapies, on the other hand, can vary.
Crown Gall Symptom and Diagnosis
Galls are most commonly found on the roots and lower branches of plants near ground level. The galls become woody and hard as they grow larger. The outer layer darkens and becomes corky. With any branch or tip dieback, the plant may be weakened and stunted. Symptoms can not appear right away after an infection. Galls grow at their fastest throughout the summer months.
Crown gall-forming bacteria can be found in the soil and can live for a long time. The bacterium is initially carried in by contaminated plants' roots. It spreads from there through soil and water movement, as well as polluted pruning tools. Bacteria enter the plant through wounds caused by chewing insects, cultivation damage, or grafting and pruning tools, among other sources.
In the absence of susceptible plants, the crown gall bacterium has been known to live in the soil for more than two years. It can survive decomposing galls buried in the soil for many years. Crown gall is more likely to be severe in limed soils than in acid soils, so soil pH can play a role in disease control.
Integrated Pest Management Strategies
1. Remove contaminated tissue with a pruner. Even if the infected plant lives for several years, the crown gall cannot be removed from it. Prune and destroy infected stems below the galled region to enhance the plant's appearance. After each cut, disinfect the pruning shears with a solution of one part bleach to nine parts water.
2. Eliminate contaminated plants. Ensure that the contaminated plant is destroyed. Since the bacterium can persist in the soil, it is important to plant a plant that is immune to it. If the same species must be planted in the same location, the soil should be removed and replaced, or soil sterilisation should be considered.
3. Cleanse the surface. Chemicals, fire, or antibiotics may be used to sterilise soils known to be contaminated with crown gall bacteria. Many home gardeners would find this impractical. A bacterium, Agrobacterium radiobacter strain 84, has been used as a biological control. Crown gall bacterium has been discovered to be antagonistic to this bacterium. It can be used as a pre-plant treatment by dipping nursery stock in a water-based suspension of live bacteria.
4. Rule out the problem. When buying forsythia and euonymus seeds, look for signs of galls. Plants with gall-forming signs should not be purchased.
Crown Gall of Apple
Apples are susceptible to a variety of galls, the worst of which is crown gall. The bacteria Rhizobium rhizogenes (old name Agrobacterium tumefaciens) causes this disease, which is likely to destroy your tree over time.
Crown gall can infect hundreds of different plants, so it can infect a variety of fruit trees. Apple, crabapple, peach, nectarine, mango, apricot, cherry, and pear are among them.
The bacteria genetically modify plants so that they can produce tumours using their own DNA. What you think of as a gall is actually a tumour that has developed on your tree.
The crown gall bacterium Agrobacterium tumefaciens can live saprophytically (living on dead organic matter) in soil for up to two years and can survive in decomposing plant debris for long periods of time. It will only continue its life cycle if it can infect and form galls on a new wound.
What are the Effects of the Infection?
The flow of nutrients and water up the stem is hampered by crown gall. Normal growth can be hampered, and your tree may begin to deteriorate. Drought stress or winter injury can make it more vulnerable.
Worst-case scenario: the growths will girdle the tree's stems or trunk, killing it completely.
What are Bacterial Galls?
The most successful cure for crown galls is to remove the gall and the bark tissue covering it after they have been exposed. Treatments that destroy or extract the bark that surrounds the gall produce excellent results. Careful surgery has been shown to be very successful in studies.
Some galls serve as "physiologic sinks," collecting resources from the surrounding plant parts and concentrating them in the gall. Galls can also provide physical protection to the insect from predators. Insect galls are typically caused by chemicals ingested into plants by insect larvae, as well as possible mechanical damage.
Plant material should be wound as little as possible. Planting too far is a bad idea. Mounding soil up around freshly planted trees is not a good idea. Keep the tree's crown as dry as possible; Agrobacterium thrives in moist conditions.