Plant endotherapy treatments enable the modification of xylem microbiome composition in olive trees

Abstract: Xylem-inhabiting plant pathogenic organisms, such as Verticillium dahliae and Xylella fastidiosa, compromise and seriously threat the health of olive crop worldwide by collapsing the xylem vessels and ultimately causing the death of the olive tree. Nowadays, the use of host resistance is the most practical and efficient control measure for vascular diseases in olive. However, research on endophytic microorganisms is gaining a special interest as a potential tool to confer protection against infection by xylem-inhabiting pathogens or suppress disease development. This work pursues i) the modification of xylem microbiome composition of cultivated olive plantlets (‘Picual’ and ‘Arbequina’) by transplanting an external xylem microbiome obtained from wild (‘Acebuche’) and cultivated (‘Picual’ and ‘Arbequina’) adult olive trees through endotherapy treatment, and ii) the evaluation of the changes in the xylem microbial composition of challenged plants over time. A total of 1,015 ASVs (grouped in 361 bacterial genera) were identified for all treatments. Globally, Massilia (12.91 %) was the most abundant genus followed by Hymenobacter (9.62 %), Sphingomonas (9.32 %), Curtobacterium (9.05 %) and Methylobacterium (6.09 %). Furthermore, alpha diversity measure showed an increase of observed ASVs after endotherapy treatment from ‘Picual’ and ‘Acebuche’ xylem sap to ‘Arbequina’ olive plantlets whereas the endotherapy inoculation of ‘Arbequina’ and ‘Acebuche’ xylematic fluid to ‘Picual’ showed the opposite behaviour. Additionally, beta diversity using ASV frequencies showed some trends across the different sampling times in each olive genotype treated. These results indicated that consortia of xylem microorganisms can be artificially inoculated in xylem vessels of seedling plants modifying their native xylem microbiome with the aim to control diseases caused by xylem-inhabiting pathogens or modify olive plant physiology and growth.