First report of Xylella fastidiosa in Italy
In mid-October 2013, the EPPO Secretariat was alerted via its Facebook page about the possible presence of Xylella fastidiosa (EPPO A1 List) on olive trees (Olea europaea) in Southern Italy by a member of the public. Shortly after, the NPPO of Italy provided information about the involvement of X. fastidiosa in the disease that is currently observed, and almost simultaneously a research team from the University of Bari and the Institute of Plant Virology (CNR) published the first results of their investigations in the Journal of Plant Pathology (Saponari et al., 2013).
Following the reporting of an extensive leaf scorch and dieback of olive trees, spreading rapidly in the area of Salento (Puglia region), the Regional Plant Protection Service promptly initiated investigations to identify the possible causal agent. These surveys were carried out in collaboration with experts from the University of Bari and the CNR. The systematic screening of samples taken from symptomatic olive trees (many of them were a century-old), revealed the presence of extensive brown discoloration of the vascular system. Portions of xylem tissue taken from symptomatic olive trees were subjected to mycological analysis by isolation on different growing media. Fungal colonies were obtained and identified by morphological and molecular tests. The results showed the constant presence of fungal species belonging to the genus Phaeoacremonium, the most frequently found species was P. parasiticum followed by P. rubrigenum, P. aleophilum and P. alvesii. Species of the genus Phaeomoniella were also isolated. According to the NPPO, this is the first time that P. parasiticum and P. alvesii have been detected on O. europaea in Italy.
In addition, these samples from olive trees were subjected to molecular analysis using specific primers for X. fastidiosa which gave positive results. The analysis was extended to almond (Prunus dulcis) and oleander (Nerium oleander) plants which were growing in the vicinity of affected olive trees and showing symptoms of leaf scorch. The results were also positive. Further serological tests (DAS-ELISA with 2 commercial kits) confirmed the presence of X. fastidiosa. The NPPO stressed that the definitive identification of the bacterium still awaits its isolation in pure culture in order to perform pathogenicity tests. In addition, further investigations are on-going to identify the bacterial strain, to evaluate its pathogenicity and identify the putative local insect vector(s). It is recalled that X. fastidiosa has an extensive natural host range (more than 100 species), including olive from which the bacterial genotype A (pathogenic to oleander and almond but not to grapevine) has been isolated in California (US).
Surveys are being carried out in Puglia to delimit the extent of the infected area. It is prohibited to move propagation material of any susceptible host species from the infected area. For the control of the disease, which does not seem to be exclusively due to X. fastidiosa, the adoption of further phytosanitary measures is currently being evaluated.
NPPO of Italy (2013-10).
Saponari M, Boscia D, Nigro F, Martelli GP (2013) Identification of DNA sequences related to Xylella fastidiosa in oleander, almond and olive trees exhibiting leaf scorch symptoms in Apulia (Southern Italy). Journal of Plant Pathology (online paper) http://sipav.org/main/jpp/index.php/jpp/article/view/2875/1549
EPPO diagnostic protocol: https://www.eppo.int/QUARANTINE/bacteria/Xylella_fastidiosa/pm7-24(1)
Pictures (on hosts other than olive): http://photos.eppo.org/index.php/album/84-xylella-fastidiosa-xylefa
Xylella fastidiosa – College of Natural Resources. http://nature.berkeley.edu/xylella/refs/index.html
Janse JD, Obradovic A (2010) Xylella fastidiosa: its biology, diagnosis, control and risks. Journal of Plant Pathology 92(1 supl.), S1.35-S1.48. http://sipav.org/main/jpp/index.php/jpp/article/view/2504/1181