Modelling the spread and control of Xylella fastidiosa in the early stages of invasion in Apulia, Italy

Abstract

Xylella fastidiosa is an important plant pathogen that attacks several plants of economic importance. Once restricted to the Americas, the bacterium, which causes olive quick decline syndrome, was discovered near Lecce, Italy in 2013. Since the initial outbreak, it has invaded 23,000 ha of olives in the Apulian Region, southern Italy, and is of great concern throughout Mediterranean basin. Therefore, predicting its spread and estimating the efficacy of control are of utmost importance. As data on this invasive infectious disease are poor, we have developed a spatially-explicit simulation model for X. fastidiosa to provide guidance for predicting spread in the early stages of invasion and inform management strategies. The model qualitatively and quantitatively predicts the patterns of spread. We model control zones currently employed in Apulia, showing that increasing buffer widths decrease infection risk beyond the control zone, but this may not halt the spread completely due to stochastic long-distance jumps caused by vector dispersal. Therefore, management practices should aim to reduce vector longdistance dispersal. We find optimal control scenarios that minimise control effort while reducing X. fastidiosa spread maximally-suggesting that increasing buffer zone widths should be favoured over surveillance efforts as control budgets increase. Our model highlights the importance of non-olive hosts which increase the spread rate of the disease and may lead to an order of magnitude increase in risk. Many aspects of X. fastidiosa disease invasion remain uncertain and hinder forecasting; we recommend future studies investigating quantification of the infection growth rate, and short and long distance dispersal.Keywords Buffer zone Á CoDiRO Á Olea europaea Á Olive quick decline syndrome Á Pierce's disease Á X. fastidiosa Electronic supplementary material The online version of this article

Impact ofXylella fastidiosasubspeciespaucain European olives

“…Consequently, our spread model simulates temporal as well as spatial spread by acknowledging the spatially explicit distribution of olive-production sites, under the assumption that alternative hosts assist dispersal through climatically suitable habitat. There is still very incomplete knowledge on the rate of spread of Xfp (31,33). While monitoring data on the outbreak in Apulia are available, the sampling design in the region drastically changed over time since the first detection.…”

“…Consequently, estimating epidemiological parameters is severely aggravated if not impossible. In addition, the observed epidemic in Apulia is likely to be a worst-case scenario due to the tight network of orchards and the abundance of suitable vectors (15,31). Therefore, extrapolating estimated parameters for Apulia to continental Europe would be questionable.…”

“…The uncertainty on various aspects was taken into consideration. First, while previous work explored the importance of long-distance jumps for the spread of Xfp (31), data to accurately parameterize such jumps are currently not available. Therefore, our spread model simplifies the dispersal process into a composite spread, comprising local dispersal and probabilistic jumps.…”

Biological Flora of the British Isles: Ulmus glabra

“…Xylella fastidiosa (Gammaproteobacteria) is known as a pest of ornamental and economic trees the USA and Taiwan (Sherald & Kostka, ), moved by sap‐sucking insects. Since 2013 several subspecies have become serious economic pests of Olea europaea and citrus trees in Europe (Azevedo, Araujo, & Lacava, ; White, Bullock, Hooftman, & Chapman, ), plus infecting species of Quercus , Platanus and Ulmus , including U. glabra where it causes bacterial leaf scorch (Sherald & Kostka, ). Ulmus species are affected by the subspecies ‘multiplex’ of X. fastidiosa (Baldi & La Porta, ).…”

Improved inference of time-varying reproduction numbers during infectious disease outbreaks

“…the epidemics of foot-and-mouth disease in 2001 and 2007 in the U.K. (Keeling et al, 2001;Ferguson et al, 2001;Keeling, 2005;Anderson, 2008)) and plants (e.g. the invasion of Italy by Xylella fastidiosa in 2013 (EFSA Panel on Plant Health, 2015;White et al, 2017)).…”