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

The spatial dynamics of Olive Quick Decline Syndrome (OQDS) caus ed 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.