Many viruses affect tulips, causing streaked flowers, mottled leaves, distorted plants and stunted growth.
What are tulip viruses?
There are at least 12 viruses that infect tulips, causing a range of symptoms, which are seen when the tulips have grown leaves in spring and early summer.
The six most important are:
- Tulip breaking virus (TBV)
- Arabis mosaic virus (ArMV)
- Tobacco rattle virus (TRV)
- Lily symptomless virus (LSV)
- Tobacco necrosis virus (TNV)
- Cucumber mosaic virus (CMV)
For more on how these viruses are transmitted, see the Biology section below.
You may see the following symptoms:
- ‘Breaks’ (streaks of a different colour) in the flowers (TBV)
- Brown, dead streaks appear in the leaves and stems (TNV)
- Mottled leaves (TRV, LSV)
- Sunken brown spots, arcs or rings in the bulbs, such bulbs give rise to stunted and distorted plants (CMV)
- Plants may be stunted, but not otherwise unaffected (ArMV, LSV)
Very little can be done to control viruses in gardens, especially those that are vectored by soil inhabiting organisms such as nematodes or Olpidium (a fungal root pathogen). The gardener’s best defence is to ensure that the bulbs come from a reputable source. Affected plants should be destroyed to prevent the spread to other tulips and other plants (some of the viruses discussed above have very wide host ranges among garden plants).
There are no chemical controls. The use of insecticides to reduce aphid transmission is not practical.
There are no chemical soil sterilants available to home gardeners for control of nematodes or Olpidium.
Plant viruses share many of the characteristics of those that infect animals, though they do not cross infect (plant viruses only infect plants). Viruses are extremely minute and consist of a protein coat and a core of nucleic acid. They have no means of self-dispersal, but rely on various vectors to transmit them from infected to healthy plants. Once viruses penetrate into the plant cells they take over the cells’ nucleic acid and protein synthesis systems and hijack them to produce more virus. They then require another vector to feed on the infected tissue and carry them to a new host.
- CMV, LSV and TBV are vectored by aphids
- ArMV and TRV are vectored by soil inhabiting nematodes
- TNV is vectored by the microscopic fungal root pathogen Olpidium brassicae
Other viruses may be vectored by other insects, mites or by mechanical transmission on pruning tools.
Tulip breaking virus (TBV) had an important role in the tulipmania, which affected the Netherlands in the seventeenth century. The break patterns in affected bulbs were highly prized and sellers commanded huge prices. Unfortunately the effect was not stable and affected bulbs did not repeat the patterns reliably in future years. Tulip varieties with these patterns are available today, but in the case of named cultivars (varieties) the breaks result from stable genetic mutation and not virus infection.