Hot water treatment causes lasting alteration to the grapevine (Vitis vinifera L.) mycobiome and reduces pathogenic species causing grapevine trunk diseases

The effective management of grapevine trunk diseases (GTDs) is an ongoing challenge. Hot water treatment (HWT) is an environmentally friendly and economically viable option; however, the short-term effects of HWT on grapevine (Vitis vinifera L.) health and production are not fully understood. The aim of this study was to compare the effects of HWT on plant growth and fungal community structure in nursery stock until plants were completely established in the field. We assessed eleven graft and three rootstock varieties from four local nurseries in a region of Catalonia (NE Spain) where GTDs are a serious threat. After treatment, the plants were left to grow under field conditions for two growing seasons. Metabarcoding of the ITS region was used to study the mycobiomes of plant graft unions and root collars. We also assessed the influence of plant physiological indicators in community composition. Hot water treatment caused lasting changes in GTD communities in both the root collar and graft union that were not always characterized as a reduction of GTD-related fungi. However, HWT reduced the relative abundance of some serious GTD-associated pathogens such as Cadophora luteo-olivacea in graft tissues, and Phaeomoniella chlamydospora and Neofusicoccum parvum in the root collar. Treatment had the greatest influence on the total and GTD-related fungal communities of Chardonnay and Xarel center dot lo, respectively. Total community variation was driven by treatment and nursery in rootstocks, whereas HWT most significantly affected the GTD community composition in R-110 rootstock. In conclusion, changes in fungal abundance were species-specific and mostly dependent on the plant tissue type; however, HWT did reduce plant biomass accumulation in the short-term.This research was partially funded by the Generalitat of Catalonia Department of Agriculture (S.B.L.). J.O. was supported by the "Ramon y Cajal" fellowship RYC-2015-17459 through the Spanish Ministry of Science and Education. D.S. was supported by the European Union's H2020 research and innovation program, under Marie Sklodowska-Curie grant agreement No 801586

Ectomycorrhizal fungi with hydrophobic mycelia and rhizomorphs dominate in young pine trees surviving experimental drought stress

Mycorrhizal fungi can help plants to cope with drought, but research on the fungal communities that are more resistant to drought or alleviate drought stress of trees is still scarce. In this study, we investigated effects of drought on soil fungal communities and explored potential fungal traits related to drought resistance under greenhouse conditions. We manipulated water availability in pine seedlings belonging to three Spanish Pinus pinaster populations from geographical areas subjected to contrasting summer drought. A set of plant ecophys-iological traits were quantified and soil fungi was quantified and profiled using ergosterol and Pacific Biosciences sequencing. Abundance of ectomycorrhizal (ECM) fungi in plants subjected to drought was lower than in well-watered plants. Most ECM taxa in plants surviving drought had long exploration types and were taxa typically forming rhizomorphs and hydrophobic mycelia. By contrast, ECM taxa in well-watered plants had wider range of distinct exploration types. No differences in fungal communities were found among P. pinaster populations. No associations between ECM fungi and plant ecophysiological traits were found, but significant interactions be-tween drought treatments and belowground plant biomass were found for the relative abundances of ECM fungi, particularly ECM with long exploration types. Plants subjected to drought may benefit by associating to ECM taxa previously shown to transport water efficiently.L.S. and R.Z. acknowledge support from Ministerio de Economía y Competitividad/FEDER Grants FUTURPIN AGL2015-68274-C3-2-R, RESILPIN RTI2018-094691-B-C33 and Xunta de Galicia-GAIN grant IN607/2021/03. J.O. was supported by a Ramón y Cajal fellowship (RYC-2015-17459) and J.A.B. was supported by the Serra-Hunter Program-Generalitat de Catalunya

Host genotype interacts with aerial spore communities and influences the needle mycobiome of Norway spruce

The factors shaping the composition of the tree mycobiome are still under investigation. We tested the effects of host genotype, site, host phenotypic traits, and air fungal spore communities on the assembly of the fungi inhabiting Norway spruce needles. We used Norway spruce clones and spore traps within the collection sites and characterized both needle and air mycobiome communities by high-throughput sequencing of the ITS2 region. The composition of the needle mycobiome differed between Norway spruce clones, and clones with high genetic similarity had a more similar mycobiome. The needle mycobiome also varied across sites and was associated with the composition of the local air mycobiome and climate. Phenotypic traits such as diameter at breast height or crown health influenced the needle mycobiome to a lesser extent than host genotype and air mycobiome. Altogether, our results suggest that the needle mycobiome is mainly driven by the host genotype in combination with the composition of the local air spore communities. Our work highlights the role of host intraspecific variation in shaping the mycobiome of trees and provides new insights on the ecological processes structuring fungal communities inhabiting woody plants.This research was supported by the Swedish research council for Environment, Agricultural Sciences and Spatial Planning, FORMAS, project 2016-00798. M.E. and H.D.C were also supported by Formas project 2017-00402. J.O. was partially supported by the 'Ramon y Cajal' fellowship RYC-2015-17459. The authors would like to thank the owners of the seed orchards, Svenska skogsplantor AB and Sodra skogsagarna AB, for allowing us to sample the trees and assisting with the air mycobiome sampling. The authors also thank Antonio Rizzi, Rena Gadjieva, Maria Jonsson, and Katarina Ihrmark for their assistance with the laboratory and field work. The authors would like to acknowledge the support of the National Genomics Infrastructure (NGI)/Uppsala, Genome Center and UPPMAX for assisting us in massive parallel sequencing and computational infrastructure. Work performed at NGI/Uppsala Genome Center was funded by RFI/VR and Science for Life Laboratory, Sweden