Science - March 3, 2005

Brassicas use virus as weapon

Researchers at Plant Research International have discovered that certain brassica plants use viruses as a weapon against the aphids that attack them. The exact mechanism is not yet fully understood, but infected aphids pass a virus on to cabbage types known as Brassica oleracea, which in turn pass the virus on to uninfected aphids.

The theory that plants can take up viruses from insects that attack them and then pass them on to uninfected attackers dates from the 1980s. Proof of the theory however did not come until Dr Manuela van Munster at Plant Research International went further with experiments she had started for her PhD research. During her earlier research Van Munster stumbled across a new virus, Myzus persicae densovirus that attacks and destroys the green peach aphid.

Van Munster discovered that infected aphids could pass the virus on to their descendants and to each other, and more intriguingly, also to aphids with which they had had no physical contact, but which had eaten off the same plant. When the researchers let isolated aphids eat on one leaf, other aphids on another leaf also became sick. That could only mean one thing: if infected aphids suck on a plant, the virus can enter the plant, and then be transported to other parts of the plant through the vascular system of the plant. The scientists conducted their experiments on a brassica plant that is not eaten, but is part of the same family as curly kale and broccoli.

Supervisor Dr Hans van den Heuvel, who now works for De Ruiter Seeds, describes the discovery as a ‘novelty’: ‘That insect viruses can stay alive in plants and find new hosts via these plants is a new discovery. It is also interesting from an evolutionary point of view, because if viruses can do this, it could mean that some plant viruses and insect viruses have a common ancestor.’ / WK