Xylem lumen: not just a Xylella playground.

Xylella outbreak in Puglia is ravaging olive plants and research is trying different paths moving through serious social and practical difficulties. The laboratory of Botany in Lecce, in collaboration with CNR ISPA local section, University of Firenze and University of Neuchatel supports the scientific community effort investigating the Olea europea xylem lumen through microscopic analysis. This apoplastic space is the channel through which the pathogen may be targeted by drugs but also a battleground on which the plant itself deploys its natural defensive barriers. In particular woody plants are able to selectively block the traffic through vessels with an active process known as tylose. It is known that tylose impairs water transport during the development of Pierce's disease (PD), caused by Xylella fastidiosa in grape. The cavitation-induced embolisms of xylem due to the bacterial colonization appears to develop before tyloses (Perez-Donoso et al 2016), anyhow both embolisms and tyloses develop with the same pattern and correlate to symptoms. Scanning Electron Microscope observations performed in the xylem of olive plants allowed the identification of different forms of xylem defects, from tylose to biotic obstructions and allowed the correct interpretation of vessels obstructions visualized at low magnification by optical microscopy and confocal microscopy. A visual screening of sections from branches of the three most representative Olea europea cultivars present in the infected area of South Puglia, Cellina di Nardò, Leccino and Ogliarola salentina, was performed. The results will be discussed. Essential bibliography Perez-Donoso, A. G., Lenhof, J. J., Pinney, K., Labavitch, J. M. (2016) Vessel embolism and tyloses in early stages of Pierce's disease. AUSTRALIAN JOURNAL OF GRAPE AND WINE RESEARCH Volume: 22 Issue: 1 Pages: 81-86