The study, published in Ecology Letters, is the first to reveal plants' ability to communicate underground in this way. If crops can be managed by exploiting this natural communication channel, it could provide a new weapon in the battle against insect pests.
Scientists from the University of Aberdeen, the James Hutton Institute and Rothamsted Research grew the bean plant (Vicia faba) in groups connected via underground networks of mycelia - a thread-like fungus that grows from one set of roots to another.
Aphids were introduced to one plant in each group, which triggering the release of a suite of chemicals designed to repel attack (see image gallery below). Remarkably, plants in the group which were not under attack themselves, but which were connected via fungal network, also began to produce the defensive chemical response. Plants without the fungal networks didn't mount a chemical defence, so remained vulnerable to aphid attack.
As previous research had shown that plants could communicate chemically through the air, researchers covered the plants to rule out above-ground signalling.
Dr David Johnson, of the University of Aberdeen, led the study. He says: "We knew that plants produce volatile chemicals when attacked, and we knew they communicate danger to each other above ground. Now we know that they communicate danger through these underground fungal networks as well."
The roots of virtually all groups of plants, including important food crops such as wheat, rice, maize and barley, are colonised by symbiotic fungi.
Another of the study's authors, Prof John Pickett of Rothamsted Research, highlighted the potential impact of this research: "Aphids affect all higher-latitude agricultural regions, including the UK, the EU, North America, and North East Asia. This research could provide a new, sustainable and natural intervention. In a field of plants that have some inducible resistance to aphids, we could use a plant that's susceptible to aphid attack to 'switch on' the defence mechanism through the natural underground connection. There's the potential to deal with other pests and diseases, in other regions, in a similar way."