The Rootstock-Scion Combination Drives Microorganisms’ Selection and Recruitment in Grapevine Rhizosphere

In the last decade, several studies demonstrated that plants have developed a tight partnership with the edaphic microbial communities, mainly bacteria, fungi, and archaea. Such microbiome accomplishes essential functions and ecological services complementary to the functions encoded by the host plant, conferring adaptive advantages to the plant, particularly during stressful conditions. The interaction between microbial communities and their host plants in the natural ecosystem are complex and the mechanisms regulating these mutualistic associations are not fully elucidated. Several biotic and abiotic factors have been shown to be important during this process, including the plant properties (species, age, stage, etc.), the soil type and agronomic practices, the geo-climate conditions, and the biotic interaction. In this context, the vineyard ecosystems represent a unique biogeography model to study and disentangle microbial biodiversity patterns (compositional diversity and potential functionality) across plants cultivated in different geographical regions. Here, I used the rhizosphere and bulk soil of seven different rootstock-scion combinations (Vitis spp.) to dissect the main factors driving the microbial communities’ recruitment in ten different vineyards in Tuscany (Italy), distributed in the Pomino and Nipozzano estates of Frescobaldi company. Among the factors investigated, I focused my attention on the geographical area, soil type and rootstock-scion combination. By using high-throughput sequencing of bacterial 16S rRNA gene and fungal ITS region, I show how both bacterial and fungal communities associated with grapevine rhizosphere and bulk soils are mainly affected by the geographical area and the soil. Nonetheless, I also revealed that the rootstock-scion combination is an important driver in shaping the microbial community, explaining a higher percentage of variability in comparison with the factors rootstock and scion taken alone. Overall, the results obtained in my thesis offer a new perspective of research that aim to develop a deep understanding about the contribution of scionrootstock combinations in the microbial community ecology of the plant holobiont. Keywords: Plant-microbe interactions, edaphic microorganisms, Microbial ecology, Plant Growth Promoting Bacteria, Rootstock-scion, Grapevine.