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The recent global re-emergence of Xylella fastidiosa (Xf) has been associated to infections on several new host species and in particular to severe infections on olive trees, reported both in Europe and southern America. Although, initial report of Xf infections on olives, caused by strains of the subsp. multiplex, from California were associated to erratic appearance of olive leaf scorching or branch desiccation, severe phenomena of decline and extensive desiccations have been repeatedly reported associated to strains of the subspecies pauca in Italy, Brazil and Argentina. Furthermore, biological and molecular studies on olives belonging to different cultivars and infected with isolates of the subsp. pauca identified cultivars with differential susceptibility and traits of resistance. In this work, we used the strain CO33 taxonomically related to subsp. sandyi, to infect olive plants of the cultivar Cellina di Nardò and Leccino, previously characterized as susceptible and resistant, respectively. Twelve months after inoculation, Xf CO33 induced twig desiccations limitedly to the inoculated plants of the cv Cellina di Nardò. Indeed, the symptomless plants of the cv Leccino harbored lower bacterial populations than cv Cellina di Nardò. Transcriptome profiling of the xylem tissues showed that Xf is sensed by plants of both cultivars with high numbers of differentially expressed genes. Among transcripts showing the highest up regulation in cv Leccino are Leucine Rich Receptor like kinases, already identified in the transcriptomes of trees infected with Xf subsp. pauca. Conversely, tissues from symptomatic plants of Cellina di Nardò display a typical defense reaction with pathogenesis related proteins among major up regulated genes. Besides extending the data on the susceptibility of olives to Xf strains of a different subspecies, the data confirm the resistance of the cv Leccino to this pathogen, supporting evidence that different mechanisms of host-pathogen interactions exist in susceptible and resistant olive cultivars. |
