Beans’ talk

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The idea that plants have developed a subterranean internet, which they use to raise the alarm when danger threatens, sounds more like the science-fiction of James Cameron’s film “Avatar” than any sort of science fact. But fact it seems to be, if work by David Johnson of the University of Aberdeen is anything to go by. For Dr Johnson believes he has shown that just such an internet, with fungal hyphae standing in for local Wi-Fi, alerts beanstalks to danger if one of their neighbours is attacked by aphids.

The experiment which suggests this was following up the discovery, made in 2010 by a Chinese team, that when a tomato plant gets infected with leaf blight, nearby plants start activating genes that help ward the infection off—even if all airflow between the plants in question has been eliminated. The researchers who conducted this study knew that soil fungi whose hyphae are symbiotic with tomatoes (providing them with minerals in exchange for food) also form a network connecting one plant to another. They speculated, though they could not prove, that molecules signalling danger were passing through this fungal network.

Dr Johnson knew from his own past work that when broad-bean plants are attacked by aphids they respond with volatile chemicals that both irritate the parasites and attract aphid-hunting wasps. He did not know, though, whether the message could spread, tomato-like, from plant to plant. So he set out to find out—and to do so in a way which would show if fungi were the messengers.

As they report in Ecology Letters, he and his colleagues set up eight “mesocosms”, each containing five beanstalks. The plants were allowed to grow for four months, and during this time every plant could interact with symbiotic fungi in the soil.

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