Viruses may sometimes cause yield losses of 10 to 30 per cent, even without the viruses being noticeable. Climate change may further increase such losses: as result of new viruses, new virus-transferring insects, and a stronger plant reaction. Scientists of Plant Research International are studying viruses and insects, as their vectors.
Plant viruses need help to spread themselves; a large number is using insects. This means that a farmer or growers must be on the alert for, e.g., virus-carrying white flies or aphids. And a warmer climate entails the serious risk that insects will be moving north while bringing along new virus diseases.
Potato virus Y, a notorious virus in potato, is transferred by aphids. Infestations with this virus have shown a considerable increase over the last decade. Our scientists are investigating the cause of those recent increases in infestations. Hundreds of different aphid species are found in the Netherlands. Each species differs in the extent to which it can transfer the virus from one plant to the other. But differences in virus transmission exist even within an aphid species (between so-called biotypes).
Possible increase by climate change
Our scientists are investigating whether climate change can play a role in the increase in infestations. Aphids are reproducing asexually throughout the year by the female giving birth to living young females. The lower temperatures before the start of the winter are inducing males to be born; sexual reproduction can take place. The female is then laying eggs on trees to bridge the winter period. Mild winters may result in males no longer be born in winter. This means that the asexual reproduction also continues in winter which in turn means that progeny are already active as potential virus vectors very early in the new year.
Conclusive information about method and time of virus transmission, and the efficiency thereof, is very important. This will be the key to ultimately reduce transmission and thus to a decease in the use of pesticides. If a farmer would already be starting with infested propagation material, the total field will be infested in a short period of time. This makes yield losses especially disastrous in countries where the potato is a staple food.
Other viruses
The scientists are of course also looking at other viruses, such as the tomato yellow leaf curl virus which is now only occurring in southern Europe but which seems to be moving north. This virus causes much damage in tomato. Until now, it has only been found once in Dutch greenhouses but the risk of infestation is increasing with climate change because the virus is hitching a ride with a new white fly species (the tobacco white fly or Bemisia tabaci) which is continually moving north under the influence of the warming climate. This new white fly is a very efficient vector of many other viruses as well; this means that there is good chance that it will also be transferring other viruses.