New insights in the ecology of boletus edulis to promote its controlled mycorrhization with cistus ladanifer plants

Resumen

Boletus edulis is one of the most appreciated fungal species due to its good edibility, generating large incomes worldwide. B. edulis is an ectomycorrhizal fungus establishing an association mainly with relatively mature forests, but it is also able to occur naturally under Cistus ladanifer as early as in 3 year-old shrublands. This observation has prompted us to consider whether a mycorrhization system could be developed to obtain prompt B. edulis sporocarps under controlled conditions. The ecosystems dominated by C. ladanifer are frequently affected by wildfires, which is detrimental to the majority of the mycorrhizal fungi associated to them. This fact has led to the need for carrying out fire prevention treatments, which may offer the opportunity of understanding what happen under different ecological scenarios. In this context, it is essential to study the interactions between the organisms intervening in the mycorrhization that are the plant, the fungus and the helper bacteria. This would allow to have a deeper knowledge of the ecology of the mycorrhizal process and link it to the production of carpophores in the field. The culture of C. ladanifer plants mycorrhized with B. edulis could be of interest in areas with poor and degraded soils, where the productivity of forested areas is very low and the economic benefit is scarce. In this sense, the crop of C. ladanifer producing B. edulis sporocarps could be regarded as an alternative culture for the most disadvantaged areas. Thus, the main objective of this thesis is to have new insights in the ecology of B. edulis as a basis to develop a protocol to produce it under controlled conditions associated to C. ladanifer shrub plants. In order to achieve this objective, we firstly studied the effect of different fire prevention treatments on both, the amount of B. edulis mycelium in the soil and the sporocarp productions. In addition, it was tested if there was a correlation between mycelium in the soil and sporocarp productions. The second study consisted of developing a first pilot assay of mycorrhization in which it was tested the effect of one recognized mycorrhizal helper bacteria on the in vitro mycorrhizal synthesis between C. ladanifer and B. edulis. A third study was conducted to test the bacterial diversity under C. ladanifer stands producers of B. edulis with Next Generation Sequencing Techniques. We analysed how fire prevention treatments affected the bacterial richness and abundance, and we tested if there was any correlation between bacteria and B. edulis mycelial biomass and sporocarp productions. Furthermore, indicator bacteria associated to the most productive B. edulis sites were identified. The fourth study consisted of carrying out a second mycorrhizal assay, this time in vivo, to test the effect of native plant growth-promoting bacteria of the C. ladanifer rhizosphere in the mycorrhizal synthesis between C. ladanifer and B. edulis. For that, several bacterial strains were isolated and characterized in order to select the best ones for the mycorrhization. The results obtained in both field studies, in which management treatments were applied, support an active forest management in these areas. Highest B. edulis mycelium amount and sporocarp productions were recorded in control and 50% clearing plots. Carrying out partial clearing treatments would optimize the production of B. edulis, reducing the potential risk and the negative effects of forest fires. Regarding the mycorrhizal assays, promising results were obtained. In the in vivo mycorrhizal assay, results were significantly improved respect to the previous mycorrhization assay. Mycorrhizal presence and level of mycorrhization increased three times when coinoculated with one of the selected native bacteria. The use of Plant Growth-Promoting Rhizobacteria could be seen as a promising tool on the production of C. ladanifer x B. edulis mycorrhized plants, and the ulterior establishment of plantations. The application of autochthonous bacteria could facilitate a better adaptation of the plant to the field. Further research is necessary to test the permanence of the obtained mycorrhizae along the time and the adaptation of the mycorrhized plants to the field. However, we believe that the results obtained in this thesis provide a first approach that can be very useful as a basis to implement a successful protocol of mycorrhization that allow the achievement of B. edulis controlled culture in the future.