Metabolic distinction of Ulmus minor xylem tissues after inoculation with Ophiostoma novo-ulmi

Dutch elm disease (DED) is the most devastating and widespread disease of elms. The pathogen, Ophiostoma novo-ulmi, spreads systemically causing xylem vessels blocking and cavitation, and ultimately resulting in the development of a wilt syndrome. Twig samples from susceptible and resistant Ulmus minor trees were harvested at 0, 5, 15, 30, 60, and 120 days post-inoculation (dpi) with O. novo-ulmi. Fourier transform-infrared (FT-IR) spectroscopy, in tandem with chemometrics, was used to monitor changes in wood chemistry as consequence of infection. Principal component analysis distinguished between spectra from inoculated and control elms, and from susceptible- and resistant-inoculated elms. By 30 dpi, infected xylem showed reduced relative levels of carbohydrates and enhanced relative levels of phenolic compounds, probably due to the degradation of cell wall polysaccharides by fungal enzymes and the synthesis of host defence compounds. On 15 dpi, samples from resistant-inoculated elms showed higher levels of starch than samples from susceptible-inoculated elms, suggesting that availability of starch reserves could affect the tree's capacity for defensive responses. The results showed the power of FT-IR spectroscopy for analysing changes in the major components of elm xylem as consequence of infection by DED, and its potential for detecting metabolic profiles related to host resistance.