Salt stress in olive tree shapes resident endophytic microbiota

Olea europea L. is a glycophyte representing one of the most important plantsin the Mediterranean area, both from an economic and agricultural point ofview. Its adaptability to different environmental conditions enables itscultivation in numerous agricultural scenarios, even on marginal areas,characterized by soils unsuitable for other crops. Salt stress represents onecurrent major threats to crop production, including olive tree. In order toovercome this constraint, several cultivars have been evaluated over the yearsusing biochemical and physiological methods to select the most suitable onesfor cultivation in harsh environments. Thus the development of novelmethodologies have provided useful tools for evaluating the adaptivecapacity of cultivars, among which the evaluation of the plant-microbiotaratio, which is important for the maintenance of plant homeostasis. In thepresent study, four olive tree cultivars (two traditional and two for intensivecultivation) were subjected to saline stress using two concentrations of salt,100 mM and 200 mM. The effects of stress on diverse cultivars were assessedby using biochemical analyses (i.e., proline, carotenoid and chlorophyllcontent), showing a cultivar-dependent response. Additionally, the olive treeresponse to stress was correlated with the leaf endophytic bacterialcommunity. Results of the metabarcoding analyses showed a significant shiftin the resident microbiome for plants subjected to moderate salt stress, whichdid not occur under extreme salt-stress conditions. In the whole, these resultsshowed that the integration of stress markers and endophytic communityrepresents a suitable approach to evaluate the adaptation of cultivars toenvironmental stresses