Detection of Xylella fastidiosa from resistant and susceptible grapevine by tissue sectioning and membrane entrapment immunofluorescence

Immunofluorescence detection was performed by tissue sectioning and membrane entrapment of Xylella fastidiosa from the inoculated hybrid selection F8909-08 (Vitis rupestris A. de Serres × V. arizonica/candicans b43-17; resistant) and Chardonnay (susceptible). In both techniques, tissue sections and bacteria-trapped polycarbonate membranes were incubated with specific polyclonal IgG and stained with fluorescein isothiocyanate (FITC)-conjugated IgG from rabbits to X. fastidiosa cells. The stained preparations were observed by fluorescence microscopy. Rapid identification of the bacteria within 3 weeks post inoculation (wpi) was possible in thin cross sections of the petioles, which allowed penetration of the specific antibody. Examination of the bacteria over time was also possible, and allowed observation of bacterial multiplication and invasion of xylem vessels. The membrane entrapment technique was able to isolate bacteria at low concentrations in infected but asymptomatic plants.