In the quest for sustainable agriculture, this thesis examines the role of biological control agents (BCAs), focusing on beneficial Pseudomonas within the cereal phytobiome. Our research began with the isolation and in vitro characterization of various Pseudomonas strains, revealing an unexpected abundance of P. sivasensis across all tested field locations and plant compartments. This led to the discovery of a new species closely related to P. sivasensis, designated P. arvensis sp. nov.

P. sivasensis strain CF10PS3 stood out for its biocontrol potential and plant colonization capabilities. A novel qPCR probe protocol was developed to specifically detect and quantify the CF10PS3 strain, distinguishing it from naturally occurring counterpart.

Strain CF10PS3 was sprayed onto wheat leaves in field to monitor its persistence in the phyllosphere and assess its impact on existing microbial communities through a newly developed bioinformatic pipeline for species-level metagenomic evaluation. The study explored the ecological effects of introducing CF10PS3, evaluating its colonization efficiency, impact on native microbiota, and its role in modifying microbial community structures crucial for plant health.

Our findings indicate that the strain CF10PS3 dynamically affects the phyllospheric microbial landscape, initially causing detriment to many species before shifting to a more balanced interaction, eventually promoting several species. These results underscore the capability of BCAs like strain CF10PS3 to act as precise microbiome modifiers, selectively enhancing beneficial microbial interactions without broadly altering overall community structure. This study advances our understanding of microbial dynamics in the phyllosphere and highlights the importance of integrating microbial management strategies into sustainable crop cultivation practices.