Epsilon Open Archive

Abstract

Secondary metabolites of the fungal ash dieback pathogen Hymenoscyphus pseudoalbidus were investigated. Nine steroidal compounds were isolated from, or detected in, liquid cultures of the fungus. Three were the previously known compounds viridiol, viridin and demethoxyviridiol. Six were the previously unreported compounds 1-deoxyviridiol, 1-deoxy-2-demethylviridiol, 3-dihydrovirone, B-norviridin enol, Bnorviridiol lactone and 1β-hydroxy-2α-hydroasterogynin A. All of the compounds are
structurally related to each other, although the three latter are B-norsteroids, which are rare in nature. Viridiol displayed phytotoxic activity to seedlings of the natural host Fraxinus excelsior. The amount of damage caused by viridiol was higher on ash seedlings of clones, classed as susceptible to H. pseudoalbidus.

The metabolomes of resistant clones of F. excelsior were compared to those of susceptible clones. No differences were detected that were common to all clones within
the groups. Metabolomes of ash seedlings treated with viridiol were compared to those of untreated ash seedlings. A number of significant changes in the concentrations of
compounds were observed at the clone level. No change common to all resistant or susceptible clones was observed.

Secondary metabolites from the bacterial biocontrol agent Pseudomonas brassicacearum MA250 were investigated. The known compounds piliferolide A and SB-253514, as well as, the previously unreported compound piliferoic acid A were
isolated from the bacterium. The compounds displayed growth inhibition of the fungal pathogen Microdochium nivale at concentrations down to 180 μM, which indicates that
they may contribute to the biocontrol effect of P. brassicacearum MA250 on M. nivale.