ABSTRACTMECHANISM OF SURFACE ESTABLISHMENT AND COLONIZATION OF BARLEY FLORETS BY FUSARIUM GRAMINEARUM ByDrew Edward AftonDespite increased research into head blight disease caused by Fusarium graminearum, little is known about the surface interactions between the fungus and its host, barley (Hordeum vulgare). Trichomes on barley florets were characterized as macro- and micro-trichomes according to previous descriptions from other grasses. These studies have identified differential interactions between macro- trichomes, which predominate vascular bundles and bract margins, and micro- trichomes, which cover the remainder of the bract surface, and F. graminearum.In infections initiated at early grain developmental stages, attachment of germinated conidia to trichomes was accompanied by growth to bract margins. In infections initiated at later developmental stages, aerial hyphae and surface colonization were reduced and infections were only observed in conjunction with trichomes. Macro-trichomes on vascular bundles provided pathways for the fungus to the vasculature below, allowing the infection to spread. Similar trichome interactions in a TRI5 knockout mutant indicated that the mycotoxin deoxynivalenol does not play a role in establishment. Furthermore, perithecia emergence from inoculated florets indicated the importance of grain developmental stage in pathogen spread, and of the vascular tissue in sexual development in later infections. Silica accumulates in grasses, commonly in the xylem, trichomes, and epidermal cells. Biogenic silica, in the form of mono-silicic acid, was shown to reduce aerial hyphae and stimulate mycotoxin production in-vitro. These results strongly implicate silica in the interactions between F. graminearum and barley.
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