| Greenhouse Plants, Ornamental -- Shoot Proliferation and Leafy Gall | |||
| Cause:
The bacterium Rhodococcus fascians is a Gram positive actinomycete. It is capable of infecting at least 44 plant families and can infect woody and herbaceous plants, both dicots and monocots. It most frequently affects herbaceous perennials. There have been field observations which imply that populations of R. fascians may persist for one or two years in soil in which diseased plants have been growing. R. fascians will also move in water, although this is a passive process as these bacteria have no ability to move on their own. On infected plants, bacteria are primarily limited to the surfaces of the leaves, petioles and stems, although some underlying cells also become infected. There is no evidence that R. fascians can systemically infect plants. The disease is primarily spread by taking cuttings from infected plants, and in infested irrigation water. The pathogen can remain viable in irrigation water for as long as 90 days in the absence of a host, and plants may become infected from either roots or foliage that has come into contact with infested water. The bacteria can be present on plant surfaces for months before symptoms develop. Wounds are not necessary for infection to occur.
Plants commonly affected include Acanthus sp. (bear’s breech), Argyranthemum sp.,Aster sp., Geranium sp. (crane’s-bill), Heuchera sp. (coral bells), Hosta sp., Iberis sp., Leucanthemum x superbum (Shasta daisy), Monarda sp., Nemesia sp., Pelargonium spp., Veronica sp., and Viola sp. There appear to be distinct differences in both the ability of various strains to infect various hosts. |
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| Symptoms: A proliferation of shoots is common with many plant species, as are leafy galls. Symptoms may be confused with those caused by crown gall bacteria (Agrobacterium tumefaciens), virus infection, herbicide damage, or eriophyid mite infestation. On hosta, abnormal bulbils form at the base of the stem. Plants affected by this bacterium often grow with less vigor, have an abnormally short stature, may produce fewer flowers, and may have less root growth, although this varies with the plant species. Plants may harbor R. fascians without showing symptoms. | |||
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Cultural
control: Disease management depends on prevention. Once the plant is introduced into a greenhouse, sanitation is
extremely important.
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| Chemical control: The bacterium can be found internally within plants to a limited extent, so topical applications of bactericides will not eradicate the bacterium. There have been no chemical trials conducted to determine efficacy of control compounds. | |||
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References: Putnam, M.L, and Miller, M.L. 2007. Rhodococcus fascians in herbaceous perennials. Plant Disease 91: 1064-1076. |
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| Content edited by: Melodie Putnam on January 1, 2009 | |||
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