Genetic differentiation of Xylella fastidiosa following the introduction into Taiwan

The economically important plant pathogen Xylella fastidiosa has been reported in multiple regions of the globe during the last two decades, threatening a growing list of crops and industries. Xylella fastidiosa subspecies fastidiosa causes disease in grapevines (Pierces disease of grapevines, PD), a current problem in the United States (US), Spain, and Taiwan. We studied PD-causing subsp. fastidiosa populations and compared the genome sequences of 33 isolates found in Central Taiwan with 171 isolates from the US and two from Spain. Phylogenetic relationships, haplotype network, and genetic diversity analyses confirm that subsp. fastidiosa was recently introduced into Taiwan from the Southeast US (i.e., the PD-I lineage in Georgia based on available data). Recent core genome recombination events were detected among introduced subsp. fastidiosa isolates in Taiwan and contributed to the development of genetic diversity, particularly in the Houli District of Taichung City in Central Taiwan. Unexpectedly, despite comprehensive sampling of all regions with high PD incidences in Taiwan, the genetic diversity observed include contributions through recombination from unknown donors, suggesting that higher diversity exists in the region. Nevertheless, no recombination event was detected between X. fastidiosa subsp. fastidiosa and the endemic sister species Xylella taiwanensis. In summary, this study improved our understanding of the genetic diversity of PD-causing subsp. fastidiosa after invasion to a new region.