A baseline of Arbutus unedo L. microbiome for future research: In vitro versus ex vitro

Abstract Arbutus unedo L. (strawberry tree) is a multipurpose Ericaceae tree with a circum-Mediterranean distribution and tolerant to abiotic and biotic stresses. The bioactive compounds and edible berries make this species attractive from an economical perspective, which causes a high demand for true to type plants. As micropropagation techniques are quite popular for the production of strawberry tree clonal plants, the characterization of its microbiome is essential, due to the possible impact in micropropagation success, including acclimatization. Thus, this study aims to identify the endophytic communities on strawberry tree plant tissues in vitro, as well as their prevalence and/or alteration upon plant acclimatization. For this purpose, the microbiome of two genotypes under micropropagation and ex vitro was identified using a culture-independent method. Bacterial OTUs were assigned to 7 phyla and 79 genera whereas only one Archaea genus was identified. The most abundant and diverse bacterial phylum was Actinobacteriota (48%) followed by Proteobacteria (43%), Firmicutes (6%) and Bacteroidota (3%). Noticeable differences in terms of composition and diversity were found when the microbiome of genotypes in vitro was compared, whereas the composition of ex vitro samples was similar. A significant higher diversity was found on both genotypes ex vitro when compared to the respective in vitro plants. This study presents the very approach into the identification and characterization of strawberry tree microbiome, including in vitro plants, using a culture-independent method. The genotype proved to be a determinant factor shaping microbiota structure. The relevance of this results for micropropagation and breeding are discussed.