## 4 Discussion  
The current study, for the first time, uncovered the structure of fungal microorganism communities colonizing the surface of sea buckthorn berries at different ripening stages in natural habitat. For a comprehensive analysis, we have applied next generation sequencing and observed the wide diversity of eukaryotic microorganisms on tested berries. The total abundance of fungal microorganisms changed significantly during the period of fruit ripening. The microbial alpha-diversity--estimated by the [PERSON]'s index, [PERSON]'s diversity index, and [PERSON]'s evenness index--was highest among the fungal community on unripe berries. The analysis of the fungal microbiota structure revealed clear differentiation between unripe and mature berries, as demonstrated by the Bray-Curtis beta-diversity  
Figure 6: Associations between blends and their components of four species of yeasts populating sea buckthorn berries. Associations are visualized by principal component analysis (PCA). (**A**) Distribution of odor blends released by _C. wieringae_ (Cw, diamond shape), _A. pullulans_ (Ap, triangle shape), _M. pulcherrina_ (Mp, square shape), and _H. warum_ (Hu, circle shape). n=5 for each species. (**B**) Distribution of volatile compounds composing the blends. Stars represent the volatile compounds indicated by numbers. Names of the compounds are listed in Table 2.  
analysis. According to our data, unripe sea buckthorn berries were dominated by _Aureobasidium_, _Taplrrina_, _Cladosporium_, and _Filobasidium_ (syn. _Cryptococcus_) genera microorganisms, while on ripe berries prevailed _Aureobasidium_ and _Metschnikowia_ (Table S1, Figure 2). It was previously demonstrated that _Cryptococcus_, _Rhodotorula_, _Sporobolomyces_, and _Aureobasidium pullulans_ yeasts were associated with the early stage of maturation of fruits and berries, such as apples, grapes, nectarines, etc. [29; 32; 42]. In our previous work, it was demonstrated that Dothioraceae family fungal microorganisms prevailed on sea buckthorn berries, which at the lower taxonomic level were attributed to uncultured _Aureobasidium_[33]. Our results were partially consistent with previous findings, since most fungal microorganisms present on sea buckthorn were represented by _Aureobasidium_. However, the overall structure of fungal microbiota varies most likely depending on the differences in climatic conditions, berry harvesting period (previously--September 2016; in this study--July 2018), localization of sea buckthorn plantation, etc. Various microorganisms act as biological control agents of phytopathogens and have a role in postharvest decay and toxin contamination by emitting volatile organic compounds [40; 43]. Several biocontrol yeasts (e.g., _Candida oleophila_, _Aureobasidium pullulans_, _Metschnikowia fructicola_, _Cryptococcus albidus_, _Saccharomyces cerevisiae_) have already been used for the production of commercial plant protection products, encouraging the deeper exploration of the fascinating traits and application possibilities of other yeasts as well [16; 44; 45]. Even the different strains of the same yeast species are able to produce highly different amounts of the same VOCs (e.g., _A. pullulans_[43]), thus it is important to investigate volatiles of yeasts strains within the species that are already proven to possess biocontrol traits (like _Aureobasidium pullulans_[43; 46], _Metschnikowia pulcherrima_[46], and _Hanseniispora uvarum_[47]), or are less investigated, but closely related to bioactive yeasts (e.g., potential biocontrol yeast _Cryptococcus wieringae_ which belongs to the same genus as _C. albidus_, _C. laurentii_, and C. flavus [16; 48; 49; 50]). _Aureobasidium pullulans_ is well-known yeast-like fungus hosting on plants, mostly present in a cooler climate like that of central Europe and less related to grapes grown in warm areas [51]. It was revealed that some _Aureobasidium_ species demonstrated biological control activity against phytopathogens, such as _Botrytis_, _Bacillus_, _Colettotrichum_, _Penicillium_[43; 52; 53].