In-Field and Early Detection of Xylella fastidiosa Infections in Olive Using a Portable Instrument

Xylella fastidiosa subsp. pauca (Xfp) is a gram-negative pathogenic bacteria responsible for serious diseases (Purcell, 2013) that inflicts considerable economic loss (Li et al., 2007; Luvisi et al., 2017). The pathogen has been linked to olive quick decline syndrome (OQDS). This devastating olive disease was first observed in Salento (Apulia, southeastern Italy) in 2009. Infected trees respond to Xfp infection with scattered desiccation of twigs and small branches in the upper crown, which extend to the rest of the canopy, showing the characteristic blight effect. The disease causes tree death within a few years from the onset of symptoms (Martelli, 2016). The primary agronomic procedure for counteracting the infection is by heavy pruning to stimulate new growth (Martelli et al., 2016).However, this does not prevent the withering and desiccation of upper vegetation in the infected tree. Lignin deposition increases the tolerance of some hosts to Xylella fastidiosa. Elevated concentration of quinic acid, a lignin precursor, less concentration of hydroxytyrosolglucoside and the up-regulation of cinnamoyl-CoA reductase and polyphenol oxidase were observed in the most tolerant olive cultivar, Leccino (Sabella et al., 2018). In this opinion article, we explore the use of a portable instrument to detect OQDS, based on the host responses at the transcript level. This approach was proposed previously to detect Huanglongbing, a severe disease affecting Citrus worldwide (Dandekar et al., 2010;Martinelli et al., 2014b). These innovative mthods of plant disease detection had been reviewed recently (Martinelli et al., 2014a).