Desert truffle cultivationnew insights into mycorrhizal symbiosis, water-stress adaptation strategies and plantation management

Abstract

Desert truffles are mycorrhizal fungi that develop hypogeus fruiting bodies and inhabit arid and semiarid areas, such as the Mediterranean basin or the Middle East. Among desert truffles genera, Terfezia and Tirmania are of special importance. The species that belong to these genera mostly establish ectendomycorrhizal symbiosis with plants of Helianthemum genus. Terfezia claveryi Chatin was the first desert truffle cultivated, using Helianthemum almeriense Pau as its host. This thesis has the objective of deepen the knowledge of desert truffles and their cultivation. To achieve this goal, five specific objectives were proposed that have resulted in several results and conclusions. In order to evaluate the role of fungal catalases in T. claveryi x H. almeriense symbiosis, a catalase, TcCAT-1, from T. claveryi ascocarps was purified to homogeneity and characterized using biochemical, chromatographic and bioinformatic techniques. In addition, transcription levels of the gene TcCAT-1 were measured by quantitative PCR. The results obtained suggest an important role of TcCAT-1 in the mycorrhization; in addition, this study has revealed the benefits of this mycorrhization in the response to water-stress. The genomes of T. claveryi and Tirmania nivea and the T. claveryi transcriptome from free living mycelium, well-watered mycorrhiza and drought-stressed mycorrhiza were sequenced and analyzed with bioinformatics tools. MAT genes have been described in these species for the first time. Furthermore, the expression pattern of plant cell wall degrading enzymes revealed a generalized downregulation of these genes under water-stress conditions. This event occurs in parallel with the type of mycorrhiza that is formed, which changes from intercellular to intracellular. In summary, the genomic and transcriptomic features described in this thesis are associated with the type of mycorrhiza and the dry environments inhabited by these species. During this thesis, data collected during 15 years of an experimental orchard of T. claveryi x H. almeriense were analyzed in order to know what environmental parameters and at what times of the year determine the production of desert truffle the most. After the statistical analysis of the data, we found that autumn first, and spring, secondly, are the key moments that determine T. claveryi yield. Specifically, the aridity index in autumn and the soil water potential from autumn to spring are the most important parameters. With this in mind, several management models are proposed. The morpho-physio-molecular responses of the H. almeriense mycorrhizal plant were characterized during spring. Using gas-exchange and molecular techniques, an abrupt phenology switch was revealed. This switch seems to be determined primarily by the vapor pressure deficit (VPD). Thanks to this, a threshold value of VPD has been established that is related to the desert truffle fructifications: in general terms, the later this threshold is reached, the higher the desert truffle yield. In order to evaluate the viability of this crop under the foreseeable increase in atmospheric CO2 concentrations in the following years, an assay was carried out. This assay consisted of growing a group of T. claveryi mycorrhizal H. almeriense plants under high concentrations of atmospheric CO2, combined with a progressive increase in water-stress conditions. The results of this assay reveal that the effects of a high atmospheric concentration of CO2 partially counteract the negative effects derived from water-stress.