Salicaceae as potential host plants ofXylella fastidiosain European temperate regions

Abstract

ABSTRACTThe discovery of three subspecies ofXylella fastidiosain Europe has triggered major attention on the potential spread up North of the bacteria. Assessing the susceptibility of a previously unexposed European flora is a key element that remains widely unknown. Under biosafety facility, we evaluated the susceptibility of Salicaceae such asPopulus tremula, Populus canescens, Salix albaandSalix capreaby mechanically inoculating the KLN59.3 GFP-labelledX. fastidiosaat 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 forX. fastidiosa, with the exception of 57% forP. canescensunder the 22 °C-growing conditions. Bacteria were detected up to 120 cm from the inoculation point forS. alba. They were detected in the roots of all species and were successfully isolated forS. albaandP. tremula. Estimates of average CFU/g of plant tissue per species ranged from 1.5E + 03 to 3.5E + 06, with the lowest figures forP. canescensand the highest forP. tremulatogether 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 Mallorca Island. There, transmission byP. spumariusof bothX. fastidiosaST1 and ST81 was proven onS. alba. We thus demonstrated that indigenous European Salicaceae such asS. albaorP. tremulaare new potential hosts forX. fastidiosa.