Salicaceae as potential host plants of Xylella fastidiosa in European temperate regions

Abstract

The discovery of several strains belonging to three subspecies of Xylella fastidiosa in Europe has triggered major attention to the potential spread up north of the bacteria. It is essential to assess the susceptibility of the previously unexposed European flora to this pathogen. Under biosafety facility, we evaluated the susceptibility of Salicaceae such as Populus tremula, Populus canescens, Salix alba and Salix caprea by mechanically inoculating the KLN59.3 GFP-labelled X. fastidiosa at 22 °C and at 28 °C. Bacterial movement and multiplication in plants were investigated by PCR, real-time PCR, confocal or scanning electron microscopy. Nine months post-inoculation, 100% of the plants tested positive for X. fastidiosa, with the exception of 57% for P. canescens under the 22 °C-growing conditions. Bacteria were detected up to 120 cm from the inoculation point for S. alba. They were detected in the roots of all species and were successfully isolated for S. alba and P. tremula. Estimates of average CFU/g of plant tissue per species ranged from 1.5E + 03 to 3.5E + 06, with the lowest figures for P. canescens and the highest for P. tremula together with high number of totally obstructed vessels observed by confocal microscopy. The possibility of insect transmission was also evaluated using an experimental set up based on Majorca Island. There, transmission by P. spumarius of both X. fastidiosa ST1 and ST81 was proven on S. alba. We thus demonstrated that indigenous European Salicaceae such as S. alba or P. tremula are new potential hosts for X. fastidiosa.