Vessel occlusion in three cultivars of Olea europaea naturally exposed to Xylella fastidiosa in open field

Abstract

Xylella fastidiosa is a Gram‐negative, xylem‐limited, bacterium which is responsible, in Italy, for the olive quick decline syndrome (OQDS). The disease is caused by the subspecies pauca and emerged a few years ago in the Apulia province of Lecce, in the Salento peninsula, on Olea europaea plants. X. fastidiosa can infect different plant species and is well known in California as the causal agent of Pierce's disease on grape. Infections of susceptible hosts with X. fastidiosa are known to result in xylem vessel occlusions, water movement impairment, and accordingly to induce the typical desiccation symptoms. In this study, we investigated xylem vessel occlusions in healthy and naturally infected O. europaea plants grown in open field by analysing three olive cultivars widespread in the region that show different degree of susceptibility to the disease: the susceptible cultivars “Ogliarola salentina” and “Cellina di Nardò,” and the tolerant cultivar “Leccino.” Our results show that occlusions were caused by tyloses and gums/pectin gels, and not by bacterial cell aggregates. Our data also indicate that occlusions are not responsible for the symptomatology of the OQDS and, as observed in Leccino plants, they are not a marker of tolerance/resistance to the disease.

The Xylella fastidiosa-Resistant Olive Cultivar “Leccino” Has Stable Endophytic Microbiota during the Olive Quick Decline Syndrome (OQDS)

“…Our samples showed an erratic distribution of X. fastidiosa, especially in the branches, confirming previous reports [25,26,41]. The taxonomic composition of the microbiota showed hundreds of families and genera, which is in agreement with the data available from other tree species [43,44].…”

Specific Fluorescence in Situ Hybridization (FISH) Test to Highlight Colonization of Xylem Vessels by Xylella fastidiosa in Naturally Infected Olive Trees (Olea europaea L.)

“…In the majority of the Xylella -colonized vessels, only a few bacterial cells or small aggregates are seen, suggesting that vessel blockage is not a colonization strategy of Xylella , but rather a consequence of endophytic colonization ( Newman et al, 2003 ). The same colonization behavior has been observed for CoDiRO strain in olive trees ( De Benedictis et al, 2017 ). Our findings in branches are similar to what was reported for olive trees, i.e., rare and solitary bacterial cells in the xylem vessels ( De Benedictis et al, 2017 ).…”

“…The same colonization behavior has been observed for CoDiRO strain in olive trees ( De Benedictis et al, 2017 ). Our findings in branches are similar to what was reported for olive trees, i.e., rare and solitary bacterial cells in the xylem vessels ( De Benedictis et al, 2017 ). Differently from De Benedictis et al (2017) , however, we found vessels blocked by large X. fastidiosa aggregates clearly visible in xylem petioles of symptomatic plants.…”

“…Xylem vessel occlusions caused by CoDiRO strain in naturally infected O. europaea plants have been observed indeed ( Cariddi et al, 2014 ) but never properly characterized and described. In particular, De Benedictis et al (2017) , using PCR-based assay and scanning electron microscopy (SEM), observed that the role played by bacterial cell aggregation in the formation of occlusions is minimal. In contrast, tyloses, gums, and pectin gels were found to be the main cause.…”

Fast Detection of Olive Trees Affected by Xylella Fastidiosa from UAVs Using Multispectral Imaging

“…From there, the bacterium spread to the northwest provinces of Brindisi and Taranto, and some infected trees have also been recently reported in the province of Bari (northeast). A large number of publications about the impact of Xf in Puglia are available; a small selection is included in the references [ 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 ].…”