Terahertz waves, electromagnetic radiation in the spectral region commonly defined between 0.3 and 10THz, allow innovative sensing and imaging techniques that can provide spectroscopic information unavailable at other wavelengths. However, simultaneously intense, broadband, and coherent spectroscopic measurement remains challenging. We report spectrometry using gases ionized by femtosecond pulses to generate and sense broadband terahertz pulses. Using a coherent heterodyne technique, the measurements span the “terahertz gap” with ⩾10% of the maximum signal from 0.3to10THz. This spectrometer, using a recycled optical probe beam and coherent detection, offers a high field strength and time-resolved measurement.

The mechanisms of resistance in barley to fusarium head blight (FHB), caused by Gibberella zeae are complex. Metabolomics technology was explored to phenotype resistance. Spikelets of barley genotypes with contrasting levels of resistance to FHB, mock inoculated or with the pathogen, were extracted with aqueous methanol and the metabolites were analyzed using liquid chromatography and hybrid mass spectrometry. Peaks were de-convoluted using XCMS and annotated using CAMERA and IntelliXtract bioinformatics tools. A t-test, of a total of 1608 purified peaks, selected 626 metabolites with significant treatment effects, of which 161 were identified as resistance related (RR) metabolites. A total of 53 metabolites, that are RR or pathogenicity related (PR), were assigned with putative compound names. These mainly belonged to three metabolic pathways: fatty acid (jasmonic acid, methyl jasmonate, 9,10-dihydroisojasmonate, linolenic acid, linoleic acid, traumatic acid), phenylpropanoid (p-coumaric acid, caffeyl alcohol, dimethoxy-4-phenylcoumarin, rosmarinic acid, diphyllin, 5-methoxypodophyllotoxin) and flavonoid (naringenin, catechin, quercetin, and alpinumisoflavone). A few PR/RR metabolites significantly reduced mycelial growth of G. zeae in vitro.

Inoculation with the virulence factor deoxynivalenol (DON) can induce disease symptoms in wheat ( Triticum aestivum L.) spikelets, even though it is not needed for the initial invasion by Fusarium graminearum Schwabe, thus the mechanism of plant defense against both the pathogen and DON, was investigated. Wheat cultivars that are resistant (‘Sumai3’) or susceptible (‘Roblin’) to fusarium head blight (FHB) were inoculated with F. graminearum, DON, or water. Inoculated spikelets were harvested 48 h after inoculation, the metabolites were extracted in methanol–water and chloroform, then derivatized and analyzed by gas chromatography – mass spectrometry. The metabolite peaks were deconvoluted and identified by manually matching the mass spectra with those in the NIST and GMD libraries. The peaks were aligned, and abundances were measured. A total of 117 metabolites were tentatively identified, including several antimicrobial metabolites and signal molecules or their precursors. Out of these 117 metabolites, 15 and 18 were identified as possible resistance-related (RR) metabolites, following F. graminearum (RRIF) and DON (RRID) inoculations, respectively, with 4 metabolites common to both. Canonical discriminant analysis of marginally significant metabolites (105) identified those with constitutive and induced resistance functions. The metabolites with high canonical loading to the canonical vectors were used to explain these functions. The putative roles of these RR metabolites in plant defense, their metabolic pathways, and their potential application for screening of wheat breeding lines for resistance to FHB are discussed.