Pelargonium viruses

What are pelargonium viruses?

Pelargonium viruses are virus diseases that affect pelargoniums. They may lead to stunted growth or cause strange flower or leaf markings. One is a notifiable quarantine organism (tomato ringspot virus, further details below)

Symptoms

Virus-infected plants may show one or more of the following symptoms;

• White streaks in the flowers, known as 'breaks'
• Yellow mottling patterns on the leaves
• Sometimes leaves develop line patterns, or ringspots
• Plants may be stunted with a general lack of vigour

Control

Non-chemical control

• If infection is suspected the plant should be destroyed – there are no cures for plant virus infection
• Old cultivars are more likely to be infected
• It is most unlikely that ordinary gardeners will encounter Tomato ringspot virus, but enthusiasts and commercial specialists should be aware of its symptoms and its quarantine status

Chemical control

There are no chemical controls for plant virus infection

Biology

Plant viruses are extremely minute pathogenic organisms similar to animal viruses, but not cross-infective: plant viruses do not infect animals. They require a mode of transport (vector), usually an invertebrate, to carry them from infected to healthy plants. Once they invade the cells of the host plant they 'hijack' its protein and nucleic acid synthetic apparatus to make more virus particles, which then in turn require a vector to move them to a new host. In the process of disrupting the plant's chemistry they produce a variety of pathogenic symptoms and reduce vigour.

The vectors for most of the pelargonium viruses are not known, but in some cases they are known to be transmitted mechanically by contact between plants and through soil. The vector in the soil is not known, although some soil-inhabiting nematodes (eelworms) are known to be vectors of other viruses. The vectors of Tomato spotted wilt virus are thrips, especially the western flower thrips Frankliniella occidentalis.

Tomato ringspot virus is not established in the UK but has been intercepted on pelargoniums imported from North America. It is vectored there by a soil inhabiting nematode which is not present in the UK, though related species are present. It causes a yellow mottling on the leaves of pelargoniums and has a wide host range. It is a notifiable quarantine organism in the UK and elsewhere in Europe. If you suspect a case, contact Plant Health at Fera.

These viruses are unlikely to be of importance to most gardeners, because commercial suppliers of plants will normally have taken steps to ensure their stocks are virus free. However, gardeners with pelargonium collections are more likely to encounter problems. Viruses are typically much more of a problem multiplied over many years by vegetative means, because infections slowly increase in stock material over the years. Many viruses are not seed borne, so new cultivars produced by hybridisation, and plants normally propagated by seed, are less affected.