Phylogenetic inference enables reconstruction of a long-overlooked outbreak of almond leaf scorch disease (Xylella fastidiosa) in Europe.

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.

Draft Genome Resources of Two Strains of Xylella fastidiosa XYL1732/17 and XYL2055/17 Isolated from Mallorca Vineyards.

Xylella fastidiosa is a plant-pathogenic bacterium that causes serious diseases in many crops of economic importance and is a quarantine organism in the European Union. This study reports a de novo-assembled draft genome sequence of the first isolates causing Pierce's disease in Europe: X. fastidiosa subsp. fastidiosa strains XYL1732/17 and XYL2055/17. Both strains were isolated from grapevines (Vitis vinifera) showing Pierce's disease symptoms at two different locations in Mallorca, Spain. The XYL1732/17 genome is 2,444,109 bp long, with a G+C content of 51.5%; it contains 2,359 open reading frames and 48 tRNA genes. The XYL2055/17 genome is 2,456,780 bp long, with a G+C content of 51.5%; it contains 2,384 open reading frames and 48 tRNA genes.