Spatial and temporal dynamics of Olive Quick Decline Syndrome in orchards in Puglia, southern Italy

On-site detection of Xylella fastidiosa in host plants and in “spy insects” using the real-time loop-mediated isothermal amplification method. (3): Abstract: The spatial dynamics of Olive Quick Decline Syndrome (OQDS) caused by X. fastidiosa subsp. pauca were determined in 20 olive plots in a selected olive growing area within the infected zone of the Lecce province, Puglia by assessing disease incidence (DI) and severity (DS) (0-5 rating scale) in June, 2016. Eight of the 20 plots with a wide range of initial DI and DS values were selected to assess the spatial and temporal dynamics of the OQDS and were evaluated in October 2016 and February 2017. Analyses are in progress and include the use of the Spatial Analysis by Distance Indices (SADIE) (Perry et al., 1999) to quantify the spatial pattern of OQDS. Spatial association between time periods was determined by the SADIE association index (Winder et al., 2001). Spatial pattern of symptomatic trees was estimated as regular (22.2% of plots), non-aggregated (33.3% of plots) or aggregated (44.4% of plots). Overall, both, DI and DS increased in the second and third assessments as compared to the initial score in June 2016 by 28.7±4.2% and 2.02±5.1% in DI, respectively; and by 0.53±0.27 and 0.04±0.06 in DS, respectively. Spatial pattern was characterized by the occurrence of several clusters of diseased trees. Increasing clustering over time was indicated by stronger values of the clustering index and the increase in patch cluster size. Spatial association was also found in the clustering of diseased trees between evaluation periods. Abstract: X. fastidiosa causes serious diseases in a broad range of woody plants (EFSA 2015). The pathogen is xylem-limited and vectored by insects. Several subspecies have been described, differing in their host range, aggressiveness, and vectors. The movement of infected plants and vectors are considered the main pathways of introduction. In 2013, olive quick decline, caused by X. fastidiosa subsp. pauca, was first reported in Apulia in south-eastern Italy (Martelli et al. 2016) and Philaenus spumarius was confirmed as the main vector. Spatio-temporal analysis can inform about the epidemiological factors driving disease distribution and may assist to limit further spread. A mechanistic model was recently developed for the early stages of X. fastidiosa invasion in Apulia (White et al. 2017). In the present study, spatio-temporal models were fitted to the distribution of X. fastidiosa in Apulia from 2013 to 2016. Different sampling strategies were followed each year, so the analysis was focused only in the Salento peninsula where a more regular sampling was observed. Bayesian inference by INLA (Rue et al. 2009) was used and the geostatistical effect was implemented by the SPDE approach (Lindgren et al. 2011). Results confirmed the high rate of disease spread under favorable environmental conditions, absence of effective vector control, and presence of highly susceptible hosts. Abstract: Since the detection of X. fastidiosa in 2015 in Corsica, France, a rather intense surveillance of infections has been carried out and has generated a total of nearly 18000 samples, 5% of which