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

The introduction of Xylella fastidiosa, a plant pathogen with a broad host range, poses a significant threat to agriculture and natural ecosystems. We analyzed six X. fastidiosa subsp. fastidiosa 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 fastidiosa, 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 X. fastidiosa on Portuguese landscapes remain largely unknown.