## 4 Discussion  
To elucidate the role of _Vitis_ genotype in microbiome assemblage, we examined the composition of epiphytic bacterial and fungal microbial communities in 36 distinct grapevine cultivars grown in the same vineyard and terroir, under the same farming system. We also characterized fluctuations of the microbial communities in different grapevine tissues and developmental stages, examining how such microbial populations change among three different phenological stages (bark and bud, berry set, and harvest) throughout the growing season. Unraveling the associated microbiomes, the relationships among them, and the impact of their hosts, could provide a tool for vine-growers and winemakers to efficiently manage microbiome structure. Here we analyzed microbiomes in a large selection of 36 cultivars grown in the same environment, including cultivars used for edible grape production as well as for wine-making and colored or white ones. Other studies focused on microbiomes inhabiting the phylospheric compartments in one [5; 10; 19; 20; 25; 34; 46], few [22], or several cultivars [23]. High-throughput sequencing revealed rich fungal or bacterial OTUs, and both similarities and differences among microbial communities between the three phenological stages were uncovered. Patterns of microbiome similarity and divergence among cultivars became evident based on PCoA visualization (Figures S1-S6). Similar patterns of microbe divergence were also detected in our previous work [17] and in other studies with different cultivars [23; 47]. In general, a core microbiome shared by all cultivars was discovered for each phenological stage. However, each cultivar hosted several different microbial species, characteristic of the host genotype. Moreover, the results revealed that some cultivars, such as Limniona (bark and bud), Agiorgitiko (berry set), and Vertzami (harvest), were unique regarding their hosted bacterial genera. Others, such as Savvatiano (bark and bud), Serifiotik (berry set), and Cabernet Sauvignon (harvest), were also unique regarding their hosted fungal genera. Several studies have documented how geography and environment affect the diversity of microbial community structure [4; 12; 46]. In our study, geographic distance was not a factor controlling microbial diversity because all cultivars were in the same vineyard. Thus, any difference observed could at least partly be considered an effect of the host genotype. Consequently, the genotype of the cultivars appeared to have a drastic impact on the microbial community, influencing the fitness of certain _V. viinifera_-associated microbes. A high percentage (79-87%) of fungal and a lower percentage (27-35%) of bacterial OTUs detected in berries could originate from barks and buds, including the majority of the dominant OTUs. Previous studies suggested that the vineyard soil may serve as an origin of primary inoculums of the plant associated microbiomes [10; 19; 21]. The detected microbial OTUs in our study include several taxa that have been typically identified in many studies across the world and suggest an important role of bark and buds as a microbial source (microbial terrori [24]) for secondary direct inoculation of other vines' aerial parts. The richness of fungal and bacterial species turned out to be lower than that discovered by [PERSON] et al. [23], who targeted similar phylospheric compartments. Additionally, the bacterial OTUs (excluding singletons) uncovered in one-season-old canes' barks and buds in this study were about 40% less than those found in our previous work [17]. The plausible explanation could be the different number of 16S RNA variable regions analyzed. All fungal OTUs discovered in this study were classified similarly to other works [22]. On the contrary, about 40% of bacterial OTUs were unclassified for harvest, 48% for berry set, and 80% for bark and bud. This large percentage of unclassified bacterial OTUs, especially for bark and buds, has been encountered in our previous work [17].