IDENTIFICATION OF DNA SEQUENCES RELATED TO XYLELLA FASTIDIOSA IN OLEANDER, ALMOND AND OLIVE TREES EXHIBITING LEAF SCORCH SYMPTOMS IN APULIA (SOUTHERN ITALY)

Abstract

Xylella fastidiosa is an important pathogen of commercial crops, landscape trees and ornamentals in North and South America. In Europe, symptoms resembling those caused by X. fastidiosa have occasionally been observed, but the presence of this EPPO quarantinable pathogen has never been confirmed. Recently, a rapidly spreading decline of aged olive trees has taken place in a large area of the Salento peninsula (Apulia, southern Italy). PCR assays on extracts from leaf veins and petioles of diseased trees gave positive reactions using X. fastidiosa gene-specific primers. In particular, PCR amplicons were generated by primers targeting the conserved hypothetical HL protein (Francis et al., 2006), the RNA polymerase sigma-70 factor, and the 16S rDNA genes (Rodrigues et al., 2003). Furthermore, molecular tests extended to almond and oleander trees with leaf scorching symptoms, growing next to diseased olive orchards, were also positive for X. fastidiosa. PCR products amplified from diseased olive trees were sequenced in duplicate and the sequences (EMBL-EBI provisional accession Nos HX2000034932- HX2000035003) showed 95 to 99% identity with the homologous genomic regions of X. fastidiosa. Tests for ascertaining the presence of X. fastidiosa by DAS-ELISA using two commercial kits (Agadia, USA and Bio-Rad, USA) were also positive, thus confirming molecular tests. Studies aimed at isolating the bacterium, determining the strain, evaluating its pathogenicity, and identifying the putative local vector(s) are currently in progress. X. fastidiosa has an extensive natural host range, including olive, from which the bacterial genotype A, pathogenic to oleander and almond, but not to grapevine, has been isolated in California (Krugner et al., 2010).