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
  These are fleshy, rounded, underground storage organs, usually sold and planted while dormant. Examples include daffodils, tulips, hyacinths, lilies, onions and garlic. The term is often used to cover other underground storage organs, including corms, tubers and rhizomes.

  bulbs give rise to stunted and distorted plants (CMV)
• Plants may be stunted, but otherwise unaffected (ArMV, LSV)

Non-chemical control

Very little can be done to control viruses in gardens, especially those that are vectored by soil-inhabiting organisms such as nematodes (eelworms) or Olpidium (a fungal root pathogen). The gardener’s best defence is to ensure that the

These are fleshy, rounded, underground storage organs, usually sold and planted while dormant. Examples include daffodils, tulips, hyacinths, lilies, onions and garlic. The term is often used to cover other underground storage organs, including corms, tubers and rhizomes.

Chemical control

There are no chemical controls. The use of insecticides to reduce aphid transmission is not practical.

There are no soil sterilants available to home gardeners for control of nematodes or Olpidium.

Plant viruses  are extremely minute infectious particles consisting of a protein coat and a core of nucleic acid. They have no means of self-dispersal, but rely on various vectors (including humans) 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.

Viruses are frequently transmitted through propagated material but, depending on the virus, can also be transmitted via insect or mite vectors, pollen, mechanical transfer via contaminated hands and tools, and nematode vectors in the soil. Some viruses can be transmitted via seed, but generally these are a minority and therefore seed propagation is often a useful way to ensure virus-free plant material.

Viruses of tulips are vectored in a number of ways

• 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 and hands.

Tulip breaking virus (TBV) played an important role in 'tulipomania', which occurred in the Netherlands in the seventeenth century. The flower break patterns in affected

These are fleshy, rounded, underground storage organs, usually sold and planted while dormant. Examples include daffodils, tulips, hyacinths, lilies, onions and garlic. The term is often used to cover other underground storage organs, including corms, tubers and rhizomes.

Genes are small sections of DNA that code for particular traits. During sexual reproduction, genes of both parents are mixed to create a genetically different offspring. Plants grown from seed may not be 'true to type' and look like their parents, but genetic variation can be beneficial, creating new, interesting characteristics and sometimes improving resilience to environmental conditions or disease. On the other hand, plants grown from cuttings are genetically identical to their parents.

genetic