Xylella fastidiosa: Host Range and Advance in Molecular Identification Techniques

Abstract

In the never ending struggle against plant pathogenic bacteria, a major goal is the early identification and classification of infecting microorganisms. Xylella fastidiosa, a Gram-negative bacterium belonging to the family Xanthmonadaceae, is no exception as this pathogen showed a broad range of vectors and host plants, many of which may carry the pathogen for a long time without showing any symptom. Till the last years, most of the diseases caused by X. fastidiosa have been reported from North and South America, but recently a widespread infection of olive quick decline syndrome caused by this fastidious pathogen appeared in Apulia (south-eastern Italy), and several cases of X. fastidiosa infection have been reported in other European Countries. At least five different subspecies of X. fastidiosa have been reported and classified: fastidiosa, multiplex, pauca, sandyi, and tashke. A sixth subspecies (morus) has been recently proposed. Therefore, it is vital to develop fast and reliable methods that allow the pathogen detection during the very early stages of infection, in order to prevent further spreading of this dangerous bacterium. To this purpose, the classical immunological methods such as ELISA and immunofluorescence are not always sensitive enough. However, PCR-based methods exploiting specific primers for the amplification of target regions of genomic DNA have been developed and are becoming a powerful tool for the detection and identification of many species of bacteria. The aim of this review is to illustrate the application of the most commonly used PCR approaches to X. fastidiosa study, ranging from classical PCR, to several PCR-based detection methods: random amplified polymorphic DNA (RAPD), quantitative real-time PCR (qRT-PCR), nested-PCR (N-PCR), immunocapture PCR (IC-PCR), short sequence repeats (SSRs, also called VNTR), single nucleotide polymorphisms (SNPs) and multilocus sequence typing (MLST). Amplification and sequence analysis of specific targets is also mentioned. The fast progresses achieved during the last years in the DNA-based classification of this pathogen are described and discussed and specific primers designed for the different methods are listed, in order to provide a concise and useful tool to all the researchers working in the field.

Biological Flora of the British Isles: Ulmus glabra

“…Ulmus species are affected by the subspecies 'multiplex' of X. fastidiosa (Baldi & La Porta, 2017). Pockets of bacterial wetwood rot in U. glabra were recorded by Lindeman (2008).…”

“…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, ). Pockets of bacterial wetwood rot in U. glabra were recorded by Lindeman ().…”

Coffee bacterial diseases: a plethora of scientific opportunities

“…Several immunological and molecular methods for specific detection of X. fastidiosa have been developed by diverse research groups (comprehensively reviewed by Baldi & La Porta ()). Some of the PCR‐based methods were designed to detect the pathogen at the species level using primers targeted to genomic regions conserved among all subspecies (Francis et al ., ), others to differentiate among a subset of subspecies (Hernandez‐Martinez et al ., ), and yet others to detect a specific subspecies (Pooler & Hartung, ; Brady et al ., ).…”

Comparison of real-time PCR and droplet digital PCR for the detection of Xylella fastidiosa in plants

“…Nowadays, different molecular tools targeting 54 specific DNA regions are available to detect the bacterium at the species level or to specifically 55 detect one of the subspecies. Conventional PCRs such as Minsavage et al (2014) have been 56 developed, but they are less sensitive than Real-Time PCR (Baldi and La Porta, 2017). Among 57 the real-time PCR techniques developed, the method designed by Harper et al (2010) was 58 identified as one of the most suitable methods for Xf detection.…”