Factores ecológicos y de gestión que afectan la producción trufera

Abstract

The mycorrhizal fungi form symbiotic associations with plants and play an important role in ecosystem processes. Mychorrizal fungi are relevant for their function for obtaining carbon compounds while providing mineral nutrition to their symbiotic host plant, but also, mycorrhizal fungi have an economic interest, by providing us with edible sporocarps. Among them, T. melanosporum is one of the most appreciated fungi in the market and its wild production and cultivation is important for rural livelihoods and landscapes in southern Europe. The main objective of this thesis was to analyse: i) the current situation of the truffle sector in the Mediterranean area; ii) the dependency of T. melanosporum productivity on rainfall variability; iii) the interactions of T. melanosporum with other soil fungi in plantations; and iv) the mating types diversity in T. melanosporum plantations. Aiming to elucidate the current situation of the truffle sector in the Mediterranean area, a total of 17 expert panellist participated in a Delphi survey where they answered a questionnaire in two of rounds. Three continuous, 49 year-long records of the annual T. melanosporum production from southern Europe’s main truffle producing regions in northeastern Spain, southern France and northcentral Italy was analysed to understand the dependency of T. melanosporum production on climate conditions. Finally, two experiments were carried out in a 1-ha experimental plantation consisting of 249 five-year-old Q. ilex inoculated with T. melanosporum planted in a recently abandoned pasture surrounded by forest located in the eastern Pre-Pyrenees; and in 29 T. melanosporum plantations from Teruel (Spain) with 3, 5, 7, 10, 14 and 20 years-old. Using several molecular techniques such as real-time PCR (qPCR), high-throughput DNA sequencing (PacBio RS II), and a patented qPCR essay (WO2012/032098) to quantify the two mating types, we describe the compositional changes of the fungal community and mating type distribution. The results obtained through the two Delphi rounds allowed us to have a complete description of the current truffle value chain and we confirmed an evolution of the sector due to the cultivation success of truffles. Due to the increase in T. melanosporum production in recent years, a trend of truffle prices decrease has been observed in the last years that have alerted the sector. To reinforce the truffle sector, highly agreed actions to develop in the future were identified. Regarding the ecological part of this thesis, it reveals how T. melanosporum production, significantly relies on previous June-August precipitation totals, while too much autumnal precipitation negatively affects winter harvest. One main concern of this thesis is if other ectomycorrhizal fungi could displace T. melanosporum in plantations and impair truffle production. We found a higher relative abundance of non-T. melanosporum ECM fungi associated with trees closer to the forest, but trees with larger root collar diameter had greater biomass of T. melanorporum mycelium and were those whose fungal community was less affected by the distance to the forest. We did not find association between T. melanosporum mycelium in the soil and distance to the forest or the abundance of non-T. melanosporum ECM fungi was observed. In the chronosequence study, we found that T. melanosporum developed steadily over the years as extraradical mycelium and T. melanosporum was not correlated with changes in other ECM fungi. Mating type frequency did not change across the years. In summary and based on these results, it can be concluded that (i) there is a need to promote the consumption of truffles, given the increase in production due to the cultivation of truffles; (ii) the T. melanosporum production significantly depends on previous summer rainfall, whereas too much autumnal precipitation has negative effects; (iii) even though the forest vicinity will influence the soil fungal community, this may have a limited effect on the growth of truffle mycelium; (iv) T. melanosporum is able to maintain colonization of the trees over the long term; (v) the initiation of the sexual reproduction is not limited by a disproportionate presence of either mating type, nor by displacement by non-T. melanosporum ECM fungi.