Effects of Tuber metabolites on the rhizospheric environment

Abstract

Several species of Tuber (Ascomycotina, Tuberales) produce a ‘burned’ area around their symbiotic plants as a result of a phytotoxic action. The volatile substances from Tuber sporophores, truffles, have been previously identified by gas chromatography coupled to gas mass spectrometry and then tested for their toxic effects on higher plants as well as soil micro-organisms. All tested organisms appeared to suffer a great inhibition when exposed to some of these substances evaporated into desiccators. Three aldehydes (2-methyl propanal, 2-methyl butanal and 3-methyl butanal) produced these effects on the two soil fungi tested ( Penicillium vinaceum and Aspergillus alliaceus ). In addition to some of these, two alcohols (2-methyl butanol and 3-methyl butanol) are also active on plants ( Triticum vulgare and Lens culinaris ). 2-Methyl butanol generally affects plants to a high degree, but the strongest effects to microfungi are caused by 3-methyl butanal. However, a strain of Pseudomonas isolated from truffle surface tolerated much higher concentrations of the three aldehydes. The substances affecting the soil micro-aerobic environment, where seeds germinate and roots live, are normal compounds of fungal metabolism produced via pyruvate pathway. Their toxic action could be a consequence of alterations caused both to the cellular membrane and to nucleic acids. The new term ‘hydnosphere’ has been proposed to define this peculiar case of soil relationships between truffle and neighbouring coenosis.