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Fusarium graminearum chemotype differences and virulence

Gerlinde Wiesenberger: University of Natural Resources and Life Sciences, Vienna

<div>In <em>F. graminearum </em>several “chemotypes” producing different trichothecene virulence factors exist. Nivalenol production seems to be the ancestral state, loss of <em>TRI13</em> leads to deoxynivalenol production. Allelic differences at <em>TRI8</em> determine whether preferentially 3-acetyl- or 15-acetyl-deoxynivalenol is produced. Recently a <em>F. graminearum</em> population was identified in North America (3-ADON genotype), which due to a different <em>TRI1</em> allele produces a novel type A-trichothecene, NX-2, lacking a C-8 keto-group. Comparing the virulence of natural isolates with different chemotypes is usually inconclusive due to abounding differences in the genomic background. We have developed positive-negative selectable transformation markers, which allow construction of near isogenic strains containing swapped alleles. Despite the fact that <em>TRI1</em> is unlinked to the core <em>TRI</em> cluster, no NX-4 producers have so far been found in nature. Introduction of the NX-<em>TRI1</em> allele into the 15-ADON background caused NX-4 production <em>in vitro</em> and drastically reduced virulence on wheat. Recently up to 20% NX-producers were detected in an area of New York State, a much higher frequency than previously reported. A selective advantage could be that NX-type toxins can escape inactivation by Michael-adduct formation with glutathione. Yet, NX toxins can undergo a non-enzymatic rearrangement to non-toxic M1-derivatives lacking the epoxide, which occurs during extended grain storage and food processing.</div>