Phytotoxic activity against <i>Bromus tectorum</i> for secondary metabolites of a seed-pathogenic <i>Fusarium</i> strain belonging to the <i>F. tricinctum</i> species complex

<p>The winter annual grass <i>Bromus tectorum</i> (cheatgrass) has become highly invasive in semiarid ecosystems of western North America. In these areas, a natural phenomenon, complete cheatgrass stand failure (‘die-off’), is apparently caused by a complex interaction among soilborne fungal pathogens. Several <i>Fusarium</i> strains belonging to the <i>Fusarium tricinctum</i> species complex were isolated from these soils and found to be pathogenic on <i>B. tectorum</i> seeds. One of these strains was produced in cheatgrass seed culture to evaluate its ability to produce phytotoxins. Six metabolites were isolated and identified by spectroscopic methods (essentially 1D and 2D NMR and ESIMS) as acuminatopyrone (<b>1</b>), blumenol A (<b>2</b>), chlamydosporol (<b>3</b>), isochlamydosporol (<b>4</b>), ergosterol (<b>5</b>) and 4-hydroxybenzaldehyde (<b>6</b>). Upon testing against <i>B.</i> <i>tectorum</i> in a seedling bioassay, (<b>6</b>) the coleoptile and radicle length of cheatgrass seedlings were significantly reduced. Compounds <b>1</b> and <b>2</b> showed moderate activity, while <b>3</b>–<b>5</b> were not significantly different from the control.</p