The endophytic bacterial community of healthy and Xylella-infected olive sapwood

Endophytic bacteria are of biotechnological and agronomic interest as they promote plant
healthiness by producing and secreting plant growth regulators, and antagonizing phytopathogens
through the induction of resistance mechanisms, and the supply of nutritional elements. One of the
factors that may influence the behavior of olive towards the ‘quick decline syndrome’ is the nature of
the endophytic microbial community occurring in sapwood. Objectives of the research was to
characterize the bacterial endophytic population occurring into the xylem of healthy and Xylellainfected olive trees by an isolation-dependent approach. Preliminary results indicate that under field
conditions, the population level of cultivable endophytic bacteria is highly variable, being mainly
affected by the host genotype, host age, and wilting severity. Among the different group are
Pseudomonas, Bacillus, Lysinibacillus, Pantoea, Microbacterium, Stenotrophomonas, and
Methylobacterium spp. Bacteria of the Methylobacetrium genus occupy the same ecological niche of X.
fastidiosa subsp. pauca. It has been reported as potential biocontrol agent of the pathogen, being its
population higher in citrus plant showing mild symptoms of variegated chlorosis. Further research is in
progress to better characterize the different Methylobacterium strains, using both biochemical and
molecular approaches, and to evaluate its activity in reducing the severity of olive quick decline
syndrome.