The hypothetical "saprotrofic phase" of the Tuber melanosporum mycelium should be permanently buried.

Since the Renaissance it has been hypothesized that truffles can grow on plant material rich in organic matter. Idea revived several times in the course of time, with the Boulanger’s proposal to cultivate the “blanche de la truffe” such as Agaricus bisporus and in time much more recent with the theory of a saprotrophic phase of the Tuber melanosporum mycelium that would feed at the expense of polyphenols, such as tannins and lignin. Hence the suggestion to fertilize truffle orchards with plant material rich in phenols and prepare mycorrhizal seedlings on phenolic substrates. The study of the genome of Tuber melanosporum (2010) has cast doubt on the possibility that its mycelium was able to implement this type of metabolism for lack of a suitable package of degradative enzymes of phenols. By using a 13C Pulse-Labeling Technique, Le Tacon et al. (2013)were able to demonstrate that the only way of carbon transfer is that from the host plant to Tuber melanosporum mycorrhizas and ascocarps. Zarivi et al. (2013) investigating the transcriptional, biochemical and histochemical of laccases expression during T. melanosporum development have added a further element against the hypothesis of saprotrophic phase. Laccases are the main enzymes for polyphenol digestion. The cDNAs of Tuber melanosporum laccases (Tmellcc1 and Tmellcc2) have been cloned. From the cloned cDNAs probes were prepared to investigate the expression levels of the Tmellcc1 and Tmellcc2 genes in the free living mycelium (FLM), ectomycorrhizas (ECM) and different developmental stages of fruit body (FB) by quantitative PCR (qPCR). The mRNA expression levels agree with the changes of laccase activities. The histochemical data agree with the qPCR and biochemical results. The highest laccase expression occurs in the ECM, when the host plant roots are invaded by the fungal mycelium, but not reaching the levels of expression such as to justify a nutritional degradation of soil polyphenols by its free living mycelium