Despite an increasing demand for Burgundy truffles (Tuber aestivum), gaps remain in our understanding of the fungus' overall lifecycle and ecology. Here, we compile evidence from three independent surveys in Hungary and Switzerland. First, we measured the weight and maturity of 2,656 T. aestivum fruit bodies from a three-day harvest in August 2014 in a highly productive orchard in Hungary. All specimens ranging between 2 and 755 g were almost evenly distributed through five maturation classes. Then, we measured the weight and maturity of another 4,795 T. aestivum fruit bodies harvested on four occasions between June and October 2015 in the same truffière. Again, different maturation stages occurred at varying fruit body size and during the entire fruiting season. Finally, the predominantly unrelated weight and maturity of 81 T. aestivum fruit bodies from four fruiting seasons between 2010 and 2013 in Switzerland confirmed the Hungarian results. The spatiotemporal coexistence of 7,532 small-ripe and large-unripe T. aestivum, which accumulate to ~182 kg, differs from species-specific associations between the size and ripeness that have been reported for other mushrooms. Although size-independent truffle maturation stages may possibly relate to the perpetual belowground environment, the role of mycelial connectivity, soil property, microclimatology, as well as other abiotic factors and a combination thereof, is still unclear. Despite its massive sample size and proof of concept, this study, together with existing literature, suggests consideration of a wider ecological and biogeographical range, as well as the complex symbiotic fungus-host interaction, to further illuminate the hidden development of belowground truffle fruit bodies.

Agrifood Research and Technology Centre of Aragon CITA Zaragoza Spain

Chair of Forest Botany Albert Ludwigs University Freiburg and Deutsche Trüffelbäume Radolfzell Germany

Chair of Forest Growth Albert Ludwigs University Freiburg Germany

CzechGlobe Research Institute CAS and Masaryk University Brno Brno Czech Republic

Department of Geography University of Cambridge Cambridge United Kingdom

European Mycological Institute EGTC EMI Soria Spain

Goethe University Frankfurt Institute for Molecular Bio Science Frankfurt Germany

INRA UMR1136 Interactions Arbres Microorganismes Champenoux France

Integrative Fungal Research Cluster Frankfurt Germany

Swiss Federal Research Institute WSL Birmensdorf Switzerland

Truffleminers Ltd Taksony Kinizsi Hungary

UMR 5175 CEFE University of Montpellier Montpellier France

Université de Lorraine UMR1136 Interactions Arbres Microorganismes Vandoeuvre lès Nancy France

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Predicted climate change will increase the truffle cultivation potential in central Europe