I wrote in other posts how brulé is formed mainly by the production of ethylene by the truffle mycelium, which has strong herbicidal effect. What we noted is just how ethylene may function as hormone with a key communication role between the truffle and the tree:
In a study done with Tuber melanosporum and Tuber borchii has been proven how the ethylene and IAA (indole-3-acetic acid) secreted by the mycelium of the truffle, cause alterations in the roots of the tree ( roots are shortened, more secondary lateral roots formed and higher amount of absorbent hairs), and all these even before there is a physical contact between the mycelia of truffles and the roots!
just read a second paper, even more interesting, about other work that study how several lima bean plants communicate with each others when they are connected by the mycelium of mycorrhizal fungi that run through their roots, just as they are attacked by aphids:
When a plant is attacked by aphids, it reports through the mycelium of fungi to their neighbors about what is happening, so that the other lima bean plants close by, secrete molecules that will protect them and also attract wasps, which are the natural predators of these aphids. The control plants without mycorrhizal fungi and thus not connected by the mycelium, have no preventive reaction to this attack by the aphids!
The metabolic pathway that allows plants such communication remain unknown, but the idea is exciting, isn’t it?
All the best,
Marcos S. Morcillo
Splivallo, R; Fischer, U; Gobel, C; Feussner, I; Karlovsky, P. 2009. Truffles Regulate Plant Root Morphogenesis via the Production of Auxin and Ethylene. PLANT PHYSIOLOGY. 150(4):2018-2029.
Babikova Z, Gilbert L, Bruce TJA, Birkett M, Caulfield JC, Woodcock C, Pickett JA, Johnson D. 2013. Underground signals carried through common mycelial networks warn neighbouring plants of aphid attack. Ecology Letters [ Early View (Online Version of Record published before inclusion in an issue