Chrysanthemum stunt viroid
Stunt is one of the most important diseases of the florist’s chrysanthemum. It has been recorded in many countries around the world, and is probably present in all chrysanthemum growing regions. The disease originated in the USA but reached Europe in the 1950s, via varieties exported to England. However, while we have lived with stunt for over four decades, in recent years the number of UK outbreaks has greatly increased and in some cases there have been considerable losses.
What is it?
The disease is caused by Chrysanthemum stunt viroid (CSVd). Viroids exist as small, circular RNA molecules which, unlike viruses, do not have a protein coat. Other examples include Potato spindle tuber viroid, which is related to CSVd but which is not found naturally on chrysanthemum. One highly significant feature of viroids is that their structure makes them exceptionally stable, allowing them to survive in sap or leaf litter for some considerable time.
What crops are affected?
The only important host of CSVd is florist’s chrysanthemum (Dendranthema morifolium). All varieties appear to be susceptible, especially all-year-round ones. CSVd has also been reported as a natural infection on Petunia hybrida var. Surfinia and Ageratum. However, neither of these are considered to be significant hosts.
What are the symptoms?
 Click on the image to view the symptoms in more detail |
In many chrysanthemum cultivars,
up to 30% of infected plants are symptomless. When symptoms are
seen, they are often variable and are highly dependent on environmental
conditions, especially temperature and light. As the name implies,
the main symptom is stunting, with a reduction of up to 50% in overall
height in mature plants. Stems also become very brittle, readily
breaking at the branch point. The other common symptoms are floral,
with infected plants having reduced flower size and demonstrating
premature flowering (up to ten days in some cases).  Stunting of affected plants of a red florist’s
chrysanthemum variety. Affected flowers in the foreground are also
showing premature opening and colour break. |
| In certain varieties, especially red-pigmented ones, symptoms can also include flower break or bleaching (a reduction in colour intensity). Foliar symptoms are less common and often pale, upright young leaves are the only indication of infection. Leaf spots or flecks, often associated with leaf distortions (‘crinkling’), are also sometimes seen. The most extreme example of this, is the symptom described as ‘measles’, which appears as large, yellow leaf blotches. |
 Click on the image to view the symptoms in more detail |
Affected flower of variety
Regal Princess Anne. The flower is reduced in size and showing marked colour bleaching. (Photograph courtesy of Prof. A.A.Brunt) 
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However, this symptom is restricted to a handful of varieties (for example ‘Mistletoe’ and ‘Bonnie Jean’) and as most of these varieties are no longer commercially available, is very rarely seen.
How is it spread?
CSVd is mainly transmitted by propagation, where cuttings have been taken from infected mother plants. However, once infected material has been introduced onto a nursery, it can be rapidly spread from plant to plant by mechanical means. This can mainly occur through the use of contaminated cutting tools, but also simply by touch or direct plant-to-plant contact. Spread via other means, such as seed or insects, is not known to occur.
How is it controlled?
The best means of controlling CSVd is to ensure that viroid-free propagating material is used. As symptoms can often be difficult to spot , laboratory-based testing is the only reliable means to ensure this. In the past, testing procedures were often not very sensitive and could take several months to complete, making the production of guaranteed clean stock difficult. However, the use of rapid, sensitive molecular methods has greatly improved this situation.
To control the disease within nurseries, good hygiene practices are necessary to prevent contact with potentially infected plants and avoid subsequent spread of the viroid. Measures include keeping tested and non-tested stock separate, restricting access to viroid-free areas, the use of disposable gloves and the regular disinfection of tools and benching.
What should I do?
If you sell florist’s chrysanthemum plants for commercial growing-on within the European Union you need to be registered with DEFRA. Plants produced by registered growers must either be no more than third generation stock from material which has been tested and found to be free from CSVd or directly derived from plants of which at least 10% have been officially inspected by the DEFRA Plant Health and Seeds Inspectorate at the time of flowering and found to be free from infection. CSVd is notifiable to DEFRA whenever it is found on registered premises.
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Department for
Environment, Food and Rural Affairs 2000 PB 5187/5188 |
CENTRAL SCIENCE LABORATORY |  |
Page last modified:
20 Nov 2006
Page published: 27 May 2004