Changes in the Structure of Strawberry Leaf Surface Bacterial and Fungal Communities by Plant Biostimulants

The application of plant biostimulants to enhance fruit quality is increasing, yet their impact on the phyllosphere microbiome remains understudied. This study investigated the effects of a sugar-based biostimulant on the bacterial and fungal communities on strawberry leaf surfaces using Illumina MiSeq sequencing. The sweetener treatment significantly decreased bacterial alpha diversity (Shannon and Simpson indices). Compositional analysis revealed a lower relative abundance of the phylum Pseudomonadota, whereas the fungal phylum Ascomycota increased and Basidiomycota decreased. At the family level, Sphingobacteriaceae, Bacillaceae, and Micrococcaceae were significantly enriched in the treated group. Furthermore, we isolated bacterial strains, including Sphingomonas zeae St1 and Frigoribacterium faeni TSAY2, which increased in abundance post-treatment and demonstrated enhanced growth using the sweetener as a sole nutrient source. These findings suggest that sugar-based biostimulants directly reshape the composition and functional potential of the phyllosphere microbiome, which may, in turn, influence nutrient uptake, plant growth, and immunity.