Lack of Linkages among Fruiting Depth, Weight, and Maturity in Irrigated Truffle Fungi Marks the Complexity of Relationships among Morphogenetic Stages

Volatilome changes during black truffle (Tuber melanosporum) ontogeny

The aroma is critical in the reproductive biology of truffles and in their commercial quality. However, previous research has almost exclusively focused on characterizing ripe ascocarps. We characterized the volatilome of the highly-prized black truffle (Tuber melanosporum) ascocarps from July, in an early development stage, to March, in the late harvesting season, and investigated the relationships among aroma, ascocarp growth and morphogenetic development. The aroma profile was analyzed using a head space gas chromatography technique coupled with mass spectrometer. Seventy-one volatile compounds were identified and three development stages were clearly distinguished according to the volatile profile. In unripe ascocarps of July-September, the profile was dominated by methanethiol (19 %), 4-penten-2-ol (11 %) and acetone (11 %), the monthly mean weight of ascocarps ranged 2-20 g, and morphogenetic stages 4-6a were prevalent. In unripe ascocarps of October-December, the most abundant volatiles were 4-penten-2-ol (21 %), methanethiol (20 %) and ethanol (13 %), the monthly mean ascocarp weight ranged 28-43 g, and morphogenetic stages 6a, 6b-c were prevalent. In ripe ascocarps (December-March), the most abundant volatiles were 4-penten-2-ol (17 %), dimethyl sulfide (16 %) and ethanol (10 %), ascocarp weight did not increase significantly, and 6b-c was practically the sole morphogenetic stage. Thirty volatiles were associated to one of these three development stages. Amongst those with higher occurrence, 4-penten-2-ol, dimethyl sulfide, ethyl acetate, 2-pentanol and 2-butanone were associated to ripe truffles, whereas methanethiol, isobutyl isobutyrate, butanedione and 3-methylanisole were associated to unripe truffles.

Eco-archaeological excavation techniques reveal snapshots of subterranean truffle growth

Despite its status as a highly-prized and coveted fungi in gastronomy, many aspects of the subterranean life cycle of the Burgundy truffle (Tuber aestivum) are still unknown, because in situ observations of the formation and maturation of truffle fruitbodies remain difficult. Here, we adopted a suite of archaeological fine-scale excavating techniques to provide unique spatiotemporal snapshots of Burgundy truffle growth at three sites in southern Germany. We also recorded the relative position, fresh weight, maturity level and genotype composition of all excavated fruitbodies. Varying by a factor of thousand, the fresh weight of 73 truffle ranged from 0.1 to 103.2 g, with individual maturity levels likely representing different life cycle stages from completely unripe to fully ripe and even decaying. While only a slightly positive relationship between fruitbody weight and maturity level was found, our results suggest that genetically distinct specimens can exhibit different life cycle stages at the same period of time and under the same environmental conditions. We therefore argue that truffles are likely able to grow, mature and ripe simultaneously between early summer and late winter of the following year. Our case study should encourage further eco-archaeological truffle excavations under different biogeographic settings and at different seasons of the year to gain deeper insights into the fungi's subterranean ecology. The expected cross-disciplinary findings will help truffle hunters and farmers to improve their harvest practices and management strategies.

Heterogeneity of the white truffle Tuber magnatum in a limited geographic area of Central-Southern Italy

Molise region (Central-Southern Italy) is one of the Italian richest areas of truffles and contributes significantly to the national production of the precious Tuber magnatum. Nevertheless, Molise truffle has received little scientific attention. Accordingly, in the present study, two T. magnatum populations collected in two different sites of Molise region were characterised from a morphological, genetic and microbiological point of view. A considerable variability between and within the two analysed groups emerged, suggesting an interesting heterogeneity of Molise white truffle populations. Ascocarps of the two groups significantly differed in size and maturation degree, although no linear correlation between weight and maturity was found. Genetic investigations focused on the Sequence-Characterised Amplified Region SCAR A21-inf. Three haplotypes, randomly distributed within the two truffle groups regardless of their collection sites, were detected. The 16S rRNA gene amplicon high-throughput sequencing provided an overview of the composition of the ascocarp-associated bacterial communities. A predominance of α-Proteobacteria was observed, with Bradyrhizobium among the main genera. However, some truffles showed unusual microbial profiles, with Pedobacter, Polaromonas and other bacterial genera as dominant taxa.