Response of Fusarium thapsinum to sorghum brown midrib lines and to phenolic metabolites
D. L. FUNNELL-HARRIS (1), S. E. Sattler (2). (1) USDA ARS, Lincoln, NE, U.S.A.; (2) USDA-ARS, Lincoln, NE, U.S.A.
Sorghum lines were bred for reduced lignin for cellulosic bioenergy uses, through the incorporation of <i>brown midrib (bmr)</i> <i>bmr6 </i>and/or <i>12</i> into two genetic backgrounds, either as single or double mutant lines. When these lines were assessed for resistance to <i>F. thapsinum </i>stalk rot, a cause of lodging, they were as resistant to <i>F. thapsinum</i> as near-isogenic wild-type lines. Peduncles of newly identified <i>bmr </i>lines from an ethyl-methanesulfonate-mutagenized population, inoculated with <i>F. thapsinum</i>, were as resistant as the wild-type line, BTx623. One <i>bmr </i>line (1107) had significantly smaller mean lesion lengths than BTx623, suggesting a mutation is associated with reduced susceptibility. Growing <i>F. thapsinum</i> on medium with ferulic, vanillic, sinapic, syringic and caffeic acids, phenolic compounds derived from the lignin pathway and elevated in different <i>bmr </i>lines, indicated that <i>F. thapsinum</i> was tolerant to these compounds. Eight sorghum fungi were also tested for effects on growth by the presence of these compounds and ferulic acid inhibited these fungi. Most of the phenolics inhibited <i>F. verticillioides </i>and <i>F. proliferatum</i>. Accumulation of phenolic metabolites in <i>bmr </i>plants may inhibit growth of some sorghum pathogens, while other factors, such as aromatic phytoalexins or salicylic acid, may be involved in resistance to <i>F. thapsinum</i>.
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