Isolation, Phylogenetic Inferences, and Early Diversification of <i>Xylella fastidiosa</i> subsp. <i>fastidiosa</i> in Cova da Beira Region, Portugal

The introduction of <i>Xylella fastidiosa</i>, a plant pathogen with a broad host range, poses a significant threat to agriculture and natural ecosystems. We analyzed six <i>X. fastidiosa</i> subsp. <i>fastidiosa</i> strains obtained from the Beira Interior region of Portugal, an area known for fruit production. Whole-genome sequencing and phylogenetic analyses were performed to genetically characterize these strains and determine their origin. The results suggest that these outbreak-demarcated areas originated from a single introduction event traced back to California, United States. All six strains belong to subspecies <i>fastidiosa</i>, sequence type 1, which has been reported to infect a variety of economically important crops, including cherry, plum, almond, and grapevine. A molecular clock analysis estimated that the introduction occurred between 2010 and 2020 (95% highest posterior density 1999 to 2022), with the strains forming a clade that diverged circa 2020. The findings underscore the importance of continued surveillance in both agricultural and unmanaged ecosystems, as the presence and potential impact of <i>X. fastidiosa</i> on Portuguese landscapes remain largely unknown.