Responses of Wheat (Triticum aestivum) Constitutively Expressing Four Different Monolignol Biosynthetic Genes to Fusarium Head Blight Caused by Fusarium graminearum

The Fusarium head blight (FHB) pathogen Fusarium graminearum produces the trichothecene mycotoxin deoxynivalenol and reduces wheat yield and grain quality. Spring wheat (Triticum aestivum) genotype CB037 was transformed with constitutive expression (CE) constructs containing sorghum (Sorghum bicolor) genes encoding monolignol biosynthetic enzymes caffeoyl coenzyme A (CoA) 3-O-methyltransferase (SbCCoAOMT), 4-coumarate-CoA ligase (Sb4CL), or coumaroyl shikimate 3-hydroxylase (SbC3 ' H) or monolignol pathway transcriptional activator SbMyb60. Spring wheats were screened for type I (resistance to initial infection, using spray inoculations) and type II (resistance to spread within the spike, using single-floret inoculations) resistances in the field (spray) and greenhouse (spray and single floret). Following field inoculations, disease index, percentage of Fusarium-damaged kernels (FDK), and deoxynivalenol measurements of CE plants were similar to or greater than those of CB037. For greenhouse inoculations, the area under the disease progress curve (AUDPC) and FDK were determined. Following screens, focus was placed on two each of SbC3 ' H and SbCCoAOMT CE lines because of trends toward a decreased AUDPC and FDK observed following single-floret inoculations. These four lines were as susceptible as CB037 following spray inoculations. However, single-floret inoculations showed that these CE lines had a significantly reduced AUDPC (P < 0.01) and FDK (P <= 0.02) compared with CB037, indicating improved type II resistance. None of these CE lines had increased acid detergent lignin compared with CB037, indicating that lignin concentration may not be a major factor in FHB resistance. The SbC3 ' H and SbCCoAOMT CE lines are valuable for investigating phenylpropanoid-based resistance to FHB.