Two Xylella fastidiosa(Xf) subsp. multiplexstrains IVIA5901 and ESVL were isolated from symptomatic almond trees in Alicante (Spain). Even if these Xf strains show an average nucleotide identity at the chromosomal level of 99.99%, they differ by the presence of two plasmids pXF64-Hb_ESVL and pUCLA-ESVL, only found in strain ESVL. Xf colonisation and disease development in host plants have been shown to be related to the size of cell aggregates, bacterial motility and biofilm formation, which are mediated by type I and type IV pili, among other traits.The goal of this study was to characterise the phenotypic characteristics of these strains that may be related to their differences in plasmid content.The Spanish Xf subsp. multiplexstrains were compared with Xf subsp. multiplexstrains Alma-Em3 and BB08-1 isolated from blueberry and the reference strain Xf subsp. fastidiosaTemecula1 from grapes, all isolated in the US. To study bacterial behaviour and phenotypic characteristics, several experiments were performed to determine adhesion force to substrate, biofilm formation, movement, cell–cell aggregation, twitching motility and patterns of bacterial growth. Additionally, a virulence assays were conducted in the greenhouse using tobacco plants cvs. SR1 and Xanthi. We also determined the presence of genes coding for type I and type IV pili in the Spanish strains. Our results show that the two Spanish isolates of Xf subsp. multiplexhave lower motility, less capacity of aggregation, make less biofilm, and cause lower disease severity when compared with the US isolates used in this study. Also, there were significant differences in disease severity between Xf Spanish strains that varied according to the tobacco cultivar, with Xanthi being the most susceptible one. Besides, our resultsindicate that strain ESVL exhibits stronger attachment to substrate than IVIA5901, but no differences in biofilm formation, cell–cell aggregation or twitching motility were found between them. The role of plasmids in the biology of these Spanish Xf strains will be further investigated.

Trabajo presentado en la 2nd European conference on Xylella fastidiosa (how research can support solutions), celebrada en Ajaccio el 29 y 30 de octubre de 2019.

Study supported by Project 727987 XF-ACTORS (EU-H2020), COST Action CA16107 EuroXanth and E-RTA2017-00004-C06-02 from AEI-INIA Spain and FEDER.

Peer reviewed