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Virus symptoms on camellia plants have been described since the late 1940's. Initially referred to as ‘Camellia leaf yellow mottle disease’, the name was changed to Camellia yellow mottle virus in the 1970’s when the symptoms were thought to be caused by a single virus. Recent DNA-based analytical methods, however, have revealed not one virus but several previously unknown viruses in camellia, some of which are likely to be responsible for some of the symptoms previously thought to be caused by Camellia yellow mottle virus. Some of the viruses may not actually cause any symptoms at all, however. Camellia yellow mottle virus is no longer considered to exist as a distinct viral species.

Symptoms associated with recently detected viruses include:

• Young leaves with chlorosis (yellowing), deformations and V-shaped margins
• Chlorotic ringspots (with and without mottle or leaf variegation)
• Necrotic (brown) rings and associated yellowing
• Variegation symptoms on leaves, sometimes also on flowers
• Leaf malformation, yellowing mosaic, yellow ringspot

There is no treatment other than to prune out affected branches. The virus symptoms do not appear to adversely affect the plant’s vigour or flowering. They may spread to other camellias in the garden, however.

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 instead 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.

Virus of camellia can all be transmitted to the next generation through propagation procedures. Information on the vectors for newly discovered camellia viruses is still to be obtained. However, from knowledge of the transmission of other viruses in the same taxonomic group it is thought that these viruses may be transmitted by mites, insect vectors and pollen.