Abstract
The insect vector borne bacterium Xylella fastidiosa was first detected in olive trees in Southern Italy in 2013, and identified as the main culprit behind the ‘olive quick decline syndrome’. Since then, the disease has spread rapidly through Italy’s main olive oil producing region. The epidemiology of the outbreak is largely unstudied, with the list of X. fastidiosa hosts and vectors in Europe likely incomplete, and the role humans play in dispersal unknown. These knowledge gaps have led to management strategies based on general assumptions that require, among others, local vector control and, in certain areas, the destruction of infected plants and healthy ones around them in an attempt to eradicate or halt the spreading pest. Here we show that, regardless of epidemiological uncertainties, the mere distribution of olive orchards in Southern Italy makes the chances of eradicating X. fastidiosa from the region extremely slim. Our results imply that Southern Italy is becoming a reservoir for X. fastidiosa. As a consequence, management strategies should keep the prevalence of X. fastidiosa in the region as low as possible, primarily through vector control, lest the pathogen, that has also been detected in southern France and the island of Mallorca (Spain), continues spreading through Italy and Europe.
Highlights
On the basis of these considerations, we assumed that X. fastidiosa can be transported by a vector between host plants that are up to 1 km apart
Using a high resolution map of olive orchards, we generated a network of potential X. fastidiosa infection pathways in Puglia by connecting all pairs of olive orchards that are within the vector’s reach, i.e. less than 1 km (μ) apart
This network, which consists of 60,886 nodes (i.e. 99.8% of mapped orchards) and 869,781 edges (Fig. 1), deliberately ignores the real possibilities of human aided long distance dispersal, of multiple, and potentially better-flying, vectors, and of other plants capable of hosting X. fastidiosa growing between olive orchards
Summary
The insect vector borne bacterium Xylella fastidiosa was first detected in olive trees in Southern Italy in 2013, and identified as the main culprit behind the ‘olive quick decline syndrome’. The fact that the LCC extends to almost the entire network, even when μ is set very conservatively, is the result of the high density and close proximity of the olive orchards in Puglia, with the distance between an orchard and its nearest neighbor (measured between the two closest points on the orchards’ perimeters) being extremely small, averaging 57 m ± 124.8 m (s.d.) and no more than 4,061 m (Fig. S2) This reveals how the topology of the original olive orchard network gives X. fastidiosa the potential to eventually reach most parts of Puglia, and establish itself in Southern Italy, as X. fastidiosa subsp. Despite the large knowledge gaps on the epidemiology and potential for control of X. fastidiosa in Europe, our analysis of the topology of the olive orchard network in Puglia and the current state of the X. fastidiosa outbreak there shows that Southern Italy is becoming a reservoir for the pathogen. Such scenarios might play out faster than research can provide remedies, network analysis can improve preparedness by elucidating opportunities, challenges, and priorities for management actions
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