Effect of Tissue on the Inoculation and Detection of Xylella fastidiosa in the Grapevine

Authors: NİHAL BUZKAN, M. ANDREW WALKER

Abstract: Pierce's disease of the grapevine is caused by a xylem-limited bacterium, Xylella fastidiosa (Xf). Susceptible vines die within a few years after infection. However, the mechanism of pathogenesis is not fully understood. It is very important to optimize the timing and positioning of inoculation in host plants to study the infection process. Rooted dormant cuttings of cv. Chardonnay (susceptible vine) were grouped as stem tissue hardening and shoot elongation for needle-inoculation with 20 µl of 2 x 10^8 cfu ml^{-1} of Xf suspension. The infected plants were sampled 2 and 3 weeks following postinoculation (wpi) at 10 cm above the point of inoculation. Negative controls were prepared with 5 plants from each group with water inoculation. DAS-ELISA was used to detect Xf. Plants with soft stem tissue were not well suited to needle inoculation due to their poorly hardened stems, and bacterial suspension could not be fully supplied to the tissue. However, ELISA worked well with both stem types. Chardonnay cuttings with ?30 cm long semi-hardwood tissue, sampled 2 wpi, resulted in fast bacterial movement, while ELISA readings dramatically dropped 3 wpi. Samples from the apical end of inoculated shoots had low ELISA readings, likely the result of young xylem development.

Keywords: Xylella fastidiosa, Pierce's disease, Grapevine, Enzyme-linked immunosorbent assay

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