Bragard, ClaudePesenti, LenaMichot, LouisLouisMichot2025-07-012025-07-012025-06-0820252025-06-10https://hdl.handle.net/2078.2/43274Xylem-invading pathogens such as Xylella fastidiosa and Brenneria salicis represent major threats to plant health due to their capacity to disrupt vascular functions, often leading to severe disease or plant death. However, the presence of bacterial endophytes within the xylem may influence the outcome of such infections. This study investigates the role of native bacterial endophytes isolated from Salicaceae species (willow and poplar) in modulating host resilience to these pathogens. Three selected endophytes from the Erwinia and Pseudomonas genera were genetically transformed to express the fluorescent marker mCherry, enabling their tracking within host tissues via confocal microscopy and molecular detection techniques. Using Nicotiana tabacum and Salix caprea as model and target hosts, respectively, experiments assessed both inoculation of endophytes and co-inoculations of endophytes and pathogens. This study confirmed that the endophytes successfully colonized host plant tissues and revealed signs of interactions with the pathogens. In Nicotiana tabacum, co-inoculation with endophytes and pathogens led to a noticeable reduction in the pathogen-induced inhibition of the host’s development, indicating a potential protective or inhibitory effect by the endophytes. In contrast, in Salix caprea, endophytes and pathogens co-inoculation had no measurable influence on plant development, indicating that under the experimental conditions, endophyte-pathogen interactions did not noticeably influence the plant’s growth parameters such as height and weight. These results reinforce the hypothesis that specific bacterial endophytes can help suppress or limit the effects of xylem-invading pathogens, offering promising avenues for biocontrol applications against diseases like Pierce's disease and watermark disease. However, while tests on model plants yielded encouraging results, those conducted on Salicaceae, the target hosts of this study, could not confirm this hypothesis, as the poor condition of the plants prior to the experiment limited the reliability of the results.EndophytesXylella fastidiosaBrenneria salicisCo-inoculationmCherryTobaccoWillow plantletstext::thesis::master thesis