Glyphosate treatments for weed control affect early stages of root colonization by Tuber melanosporum but not secondary colonization

Sequential application of inoculation methods improves mycorrhization of Quercus ilex seedlings by Tuber melanosporum

The use of mycorrhized seedlings has been critical to the success of modern truffle cultivation, which nowadays supplies most European black truffles (Tuber melanosporum) to markets. Ascospore inoculation has been traditionally used to produce these seedlings, but little scientific information is publicly available on the inoculation methods applied or on the possibility of combining them. We evaluated the potential of sequential inoculation for the controlled colonization of holm oak fine roots by T. melanosporum, with two different nursery assays and a full factorial design. Three inoculation methods were sequentially applied: radicle inoculation, inoculation of the substrate in seedling trays and inoculation of the substrate in the final pot. Despite the differences in the results of the two assays, which suggest that cultivation conditions and/or the timing of nursery operations may influence the relative effectiveness of inoculation methods, the sequential application appeared as an effective and realistic alternative for commercial inoculation of holm oak seedlings with T. melanosporum. The increase in the amount of inoculum applied with each inoculation method improved the mycorrhizal colonization of seedlings, whereas separately none of the inoculation methods appeared clearly superior to the other ones. The depth distribution of truffle mycorrhizae pointed that the inoculation in the final pot was more effective than other methods in lower parts of the root system, whereas the early inoculation appeared more effective to reduce the occurrence of the opportunist ectomycorrhizal fungus Sphaerosporella brunnea.

Ecosystem consequences of herbicides: the role of microbiome

Non-target organisms are globally exposed to herbicides. While many herbicides - for example, glyphosate - were initially considered safe, increasing evidence demonstrates that they have profound effects on ecosystem functions via altered microbial communities. We provide a comprehensive framework on how herbicide residues may modulate ecosystem-level outcomes via alteration of microbiomes. The changes in soil microbiome are likely to influence key nutrient cycling and plant-soil processes. Herbicide-altered microbiome affects plant and animal performance and can influence trophic interactions such as herbivory and pollination. These changes are expected to lead to ecosystem and even evolutionary consequences for both microbes and hosts. Tackling the threats caused by agrochemicals to ecosystem functions and services requires tools and solutions based on a comprehensive understanding of microbe-mediated risks.

Intraspecific Competition Results in Reduced Evenness of Tuber melanosporum Mating-Type Abundance from the Nursery Stage

The highly prized black truffle is a fungus mostly harvested in orchards planted with mycorrhizal seedlings. It is an obligatory outcrossing fungus with a single MAT locus containing two alternative mating-type idiomorphs. In the orchards, at the mycorrhizal level, these mating types are frequently spatially segregated. Some studies found that this segregation was pronounced from the nursery stage, whereas others did not find such a marked segregation. Besides, information on the host tree species and nursery conditions used in Spain, one of the main truffle-producing countries, are very scarce. In this study, we investigated the temporal dynamics of mating types in nursery seedlings of Quercus ilex and Quercus faginea, as well as the influence of cultural conditions in the nursery. Our results indicated that at the plant level, there was a trend for one of the mating types to dominate over the other from the first to the second year in the nursery, in both host species and both nursery conditions tested. However, this segregation process was not so sharp as previously reported. Our results support the hypothesis that intraspecific competition results in reduced evenness of mating-type abundance from the nursery stage, although almost all seedlings maintained both mating types and, at the seedling batch scale, the occurrence of both mating types was roughly balanced.

White mulch and irrigation increase black truffle soil mycelium when competing with summer truffle in young truffle orchards

The black truffle (Tuber melanosporum Vittad.) and the summer truffle (Tuber aestivum Vittad.) are two of the most appreciated edible fungi worldwide. The natural distributions of both species partially overlap. However, the interspecific interactions between these truffles and how irrigation and mulching techniques impact the dynamics between them are still unknown. Here, an experimental truffle plantation with Quercus ilex was established in Maials (Catalonia, Spain), combining three soil mulch treatments (white mulch, black mulch and bare soil as a control) and two irrigation regimes (irrigated and non-irrigated as a control) to investigate truffle mycelial dynamics in soil when both truffle species co-occur. The development of truffle mycelium in two different seasons (spring and autumn) in two consecutive years (2017 and 2018) was quantified using qPCR. Truffle mycelia of both species showed greatest development under white mulch. When mycelia of both truffle species co-occurred in soil, irrigation combined with white mulch resulted in greater quantities of T. melanosporum mycelial biomass, whereas the control irrigation treatment favoured the development of T. aestivum. Mulch treatments were also advantageous for seedling growth, which was expressed as root collar diameter and its increment during the study period. Significant relationships between root collar diameter and root growth and the amount of mycelial biomass in the soil were observed for both truffle species. Our results indicate the potential advantages of using white mulch to support irrigation in truffle plantations located in areas with dry Mediterranean climatic conditions to promote the development of Tuber mycelium.