Xylella fastidiosa, a quarantine organism in the European Union (EU), causes diseases in a wide variety of plants such as almond, cherry, grape, citrus, elm, olive, and coffee trees and many ornamental plants. Since the detection of the bacterium in Italy (2013), where it is associated to a severe epidemic on olive trees, the pathogen has also been detected in France (2015) and Germany (2016) (EPPO 2016).
The recent introductions of the bacterium Xylella fastidiosa (Xf) into Europe are linked to the international plant trade. However, both how and when these entries occurred remains poorly understood. Here, we show how almond scorch leaf disease, which affects ~79% of almond trees in Majorca (Spain) and was previously attributed to fungal pathogens, was in fact triggered by the introduction of Xf around 1993 and subsequently spread to grapevines (Pierce's disease). We reconstructed the progression of almond leaf scorch disease by using broad phylogenetic evidence supported by epidemiological data. Bayesian phylogenetic inference predicted that both Xf subspecies found in Majorca, fastidiosa ST1 (95% highest posterior density, HPD: 1990–1997) and multiplex ST81 (95% HPD: 1991–1998), shared their most recent common ancestors with Californian Xf populations associated with almonds and grapevines. Consistent with this chronology, Xf-DNA infections were identified in tree rings dating to 1998. Our findings uncover a previously unknown scenario in Europe and reveal how Pierce's disease reached the continent. ; This work was partially funded by projects XF-ACTORS (Xylella fastidiosa Active Containment Through a Multidisciplinary-Oriented Research Strategy; grant 727987 from European Union's Horizon 2020 Framework Research Programme) and ERTA2017-00004-02 and E-RTA2017-00004-04 (Desarrollo de estrategias de erradicación, contención y control de X. fastidiosa en España) from 'Programa Estatal de I + D + I Orientada a los Retos de la Sociedad of the Spanish Government' and FEDER) and from the Organización Profesional del Aceite de Oliva Español'. M.P.V-A. was recipient of a PhD fellowship from Intramural Project 201840E111from CSIC. A.B. was recipient of a postdoctoral UIB contract funded by the Vicerectorado de Investigación e Internacionalización of the University of the Balearic Islands.
Xylella fastidiosa (Xf) is a vascular plant pathogen native to the Americas. In 2013, it was first reported in Europe, implicated in a massive die-off of olive trees in Apulia, Italy. This finding prompted mandatory surveys across Europe, successively revealing that the bacterium was already established in some distant areas of the western Mediterranean. To date, the Balearic Islands (Spain) hold the major known genetic diversity of Xf in Europe. Since October 2016, four sequence types (ST) belonging to the subspecies fastidiosa (ST1), multiplex (ST7, ST81), and pauca (ST80) have been identified infecting 28 host species, including grapevines, almond, olive, and fig trees. ST1 causes Pierce's disease (PD) and together with ST81 are responsible for almond leaf scorch disease (ALSD) in California, from where they were introduced into Mallorca in around 1993, very likely via infected almond scions brought for grafting. To date, almond leaf scorch disease affects over 81% of almond trees and Pierce's disease is widespread in vineyards across Mallorca, although producing on average little economic impact. In this perspective, we present and analyze a large Xf-hosts database accumulated over four years of field surveys, laboratory sample analyses, and research to understand the underlying causes of Xf emergence and spread among crops and wild plants in the Balearic Islands. The impact of Xf on the landscape is discussed. ; This work was partially funded by projects XF-ACTORS (Xylella fastidiosa Active Containment Through a Multidisciplinary-Oriented Research Strategy; grant 727987 from the European Union's Horizon 2020 Framework Research Programme), ERTA2017-00004-02 and E-RTA2017-00004-04 (Desarrollo de estrategias de erradicación, contención y control de X. fastidiosa en España) from 'Programa Estatal de I + D + I Orientada a los Retos de la Sociedad of the Spanish Government' and FEDER), the Spanish olive oil Interprofesional and the Ministry of Agriculture, Fisheries and Food and the Project ITS2017-095 from 'Consejeria de Medio Ambiente, Agricultura y Pesca' from the Balearic Islands, Spain. M.P.V-A. was a recipient of a PhD fellowship from Intramural Project 201840E111 from CSIC.
[EN] Two hundred and twenty-fiveDiaportheisolates were collected from 2005 to 2019 in almond orchards showing twig cankers and shoot blight symptoms in five different regions across Spain. Multilocus DNA sequence analysis with five loci (ITS,tub,tef-1 alpha,calandhis), allowed the identification of four knownDiaporthespecies, namely:D. amygdali,D. eres,D. foeniculinaandD. phaseolorum. Moreover, a novel phylogenetic species,D. mediterranea, was described.Diaportheamygdaliwas the most prevalent species, due to the largest number of isolates (85.3%) obtained from all sampled regions. The second most frequent species wasD. foeniculina(10.2%), followed byD. mediterranea(3.6%),D.eresandD. phaseolorum, each with only one isolate. Pathogenicity tests were performed using one-year-old almond twigs cv. Vayro and representative isolates of the different species. Except forD. foeniculinaandD. phaseolorum, allDiaporthespecies were able to cause lesions significantly different from those developed on the uninoculated controls.Diaporthe mediterraneacaused the most severe symptoms. These results confirmD. amygdalias a key pathogen of almonds in Spain. Moreover, the new species,D. mediterranea, should also be considered as a potential important causal agent of twig cankers and shoot blight on this crop. ; Research funded by the Instituto Nacional de Investigacion y Tecnologia Agraria y Alimentaria (INIA), grants RTA2017-00009-C04-01, -02, -03 and -04 and with matching funds from the European Regional Development Fund (ERDF). G. Elena and C. Agusti-Brisach were supported by the Spanish post-doctoral grants "Juan de la Cierva-Formacion" and "Juan de la Cierva-Incorporacion", respectively. J. Luque and X. Miarnau were partially supported by the CERCA program, Generalitat de Catalunya. D. Gramaje was supported by the Ramon y Cajal program, Spanish Government (RYC-2017-23098). ; León Santana, M.; Berbegal Martinez, M.; Rodríguez-Reina, JM.; Elena, G.; Abad Campos, P.; Ramón-Albalat, A.; Olmo, D. (2020). Identification and ...
