Fig. 6: Time-calibrated maximum clade credibility tree from a combination of two runs of 500 million states and 50 million burn-ins based on core-genome sequences for isolates of Xylella fastidiosa (Xf) subsp. multiplex from Majorca, Alicante, Corsica and California (including isolate Griffins from Georgia, USA).

The node of the mid-root tree represents the source population from California from which the European clades are derived. Strong informative priors are described in Table 1. were used to calibrate the clade nodes. The model is congruent with the temporal expansion of the almond leaf scorch disease (ALSD) in California (1930s–1980s⁹), the likely introduction of Xf ST81 in Majorca around 1993, and the time of introduction in Corsica proposed by Soubeyrand et al.⁵⁴ and the more recent epidemic of ALSD in Alicante (Spain). Node bars = 95% highest posterior density (HPD) node age; node number represents the posterior probability. Subtrees of each clade were collapsed to mask artificial long branches due to trade-offs between tree prior node ages and substitution rates.