The agriculturally important genus Colletotrichum is an emerging model pathogen for studying defense in Arabidopsis. During the process of screening for novel pathogenic Colletotrichum isolates on Arabidopsis, we found significant differences in defense responses between detached and attached leaf assays. A near-adapted isolate Colletotrichum linicola A1 could launch a typical infection only on detached, but not attached, Arabidopsis leaves. Remarkably, resistance gene-like locus RCH1-mediated resistance in intact plants also was compromised in detached leaves during the attacks with the virulent reference isolate C. higginsianum. The differences in symptom development between the detached leaf and intact plant assays were further confirmed on defense-defective mutants following inoculation with C. higginsianum, where the greatest inconsistency occurred on ethylene-insensitive mutants. In intact Arabidopsis plants, both the salicylic acid- and ethylene-dependent pathways were required for resistance to C. higginsianum and were associated with induced expression of pathogenesis-related genes PR1 and PDF1.2. In contrast, disease symptom development in detached leaves appeared to be uncoupled from these defense pathways and more closely associated with senescence: an observation substantiated by coordinated gene expression analysis and disease symptom development, and chemically and genetically mimicking senescence.

BackgroundFusarium head blight (FHB), a scab principally caused by Fusarium graminearum Schw., is a serious disease of wheat. The purpose of this study is to evaluate the potential of combining synchrotron based phase contrast X-ray imaging (PCI) with Fourier Transform mid infrared (FTIR) spectroscopy to understand the mechanisms of resistance to FHB by resistant wheat cultivars. Our hypothesis is that structural and biochemical differences between resistant and susceptible cultivars play a significant role in developing resistance to FHB.ResultsSynchrotron based PCI images and FTIR absorption spectra (4000–800 cm−1) of the floret and rachis from Fusarium-damaged and undamaged spikes of the resistant cultivar ‘Sumai3’, tolerant cultivar ‘FL62R1’, and susceptible cultivar ‘Muchmore’ were collected and analyzed. The PCI images show significant differences between infected and non-infected florets and rachises of different wheat cultivars. However, no pronounced difference between non-inoculated resistant and susceptible cultivar in terms of floret structures could be determined due to the complexity of the internal structures. The FTIR spectra showed significant variability between infected and non-infected floret and rachis of the wheat cultivars. The changes in absorption wavenumbers following pathogenic infection were mostly in the spectral range from 1800–800 cm−1. The Principal Component Analysis (PCA) was also used to determine the significant chemical changes inside floret and rachis when exposed to the FHB disease stress to understand the plant response mechanism. In the floret and rachis samples, PCA of FTIR spectra revealed differences in cell wall related polysaccharides. In the florets, absorption peaks for Amide I, cellulose, hemicellulose and pectin were affected by the pathogenic fungus. In the rachis of the wheat cultivars, PCA underlines significant changes in pectin, cellulose, and hemicellulose characteristic absorption spectra. Amide II and lignin absorption peaks, persistent in the rachis of Sumai3, together with increased peak shift at 1245 cm−1 after infection with FHB may be a marker for stress response in which the cell wall compounds related to pathways for lignification are increased.ConclusionsSynchrotron based PCI combined with FTIR spectroscopy show promising results related to FHB in wheat. The combined technique is a powerful new tool for internal visualisation and biomolecular monitoring before and during plant-microbe interactions to understand both the differences between cultivars and their different responses to disease stress.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0357-5) contains supplementary material, which is available to authorized users.

Metabolic changes in spikelets of wheat varieties FL62R1, Stettler, Muchmore and Sumai3 following Fusarium graminearum infection were explored using NMR analysis. Extensive 1D and 2D 1H NMR measurements provided information for detailed metabolite assignment and quantification leading to possible metabolic markers discriminating resistance level in wheat subtypes. In addition, metabolic changes that are observed in all studied varieties as well as wheat variety specific changes have been determined and discussed. A new method for metabolite quantification from NMR data that automatically aligns spectra of standards and samples prior to quantification using multivariate linear regression optimization of spectra of assigned metabolites to samples’ 1D spectra is described and utilized. Fusarium infection-induced metabolic changes in different wheat varieties are discussed in the context of metabolic network and resistance.

Colletotrichum truncatum (CT) is a fungus with the potential for biocontrol of the noxious weed scentless chamomile in western Canada. This fungus is morphologically identical to the anthracnose pathogen of lentil and has occasionally caused slight disease symptoms on lentil in controlled conditions, posing crop safety concern. This study was conducted to better understand the risk and potential infection strategy of the biocontrol agent on the most important pulse crops in western Canada. Inoculation trials were carried out on young plants (3-4 weeks from seeding) and detached leaves from these plants in a greenhouse to determine consistency of cross infection and examine detailed infection processes. The CT isolates from scentless chamomile caused visible disease symptoms only on scentless chamomile, but not on lentil or field pea 14 days post inoculation. Lentil CT isolates caused severe disease on lentil and field pea, but no symptoms on scentless chamomile. Microscopic examinations of inoculated leaves at post-inoculation intervals showed a hemibiotrophic infection process with both chamomile and lentil isolates on their respective hosts, with rapid production of infection vesicles and primary hyphae in epidermal cells that remained alive until the development of secondary hyphae. These infection structures were neither observed in lentil leaves inoculated with chamomile CT isolates, nor vice versa. The initiation of secondary hyphae generally coincided with onset of symptoms on scentless chamomile or lentil plants. Chamomile CT isolates were recovered from 2%-23% of surface-sterilized symptomless lentil leaves incubated on a paraquat agar, and this indicates endophytic colonization or potential latent infection by the chamomile CT in lentil. The possible nature of this quiescent colonization in lentil by the chamomile CT is discussed. Résumé : Colletotrichum truncatum (CT) est un champignon qui présente du potentiel sur le plan de la lutte biologique antiparasitaire contre la matricaire inodore, une mauvaise herbe nuisible de l'Ouest canadien. Ce champignon est morphologiquement identique à l'agent pathogène causant l'anthracnose chez la lentille et qui a, à l'occasion, sous conditions contrôlées, provoquer de légers symptômes chez, ce qui suscite certaines préoccupations sur le plan de la sécurité. Cette étude a été menée afin de mieux comprendre la stratégie potentielle d'infection de l'agent de lutte biologique antiparasitaire et le risque qu'il représente pour les plus importantes légumineuses cultivées dans l'Ouest canadien. Des essais d'inoculation ont été menés en serre sur de jeunes plants de 3 à 4 semaines et sur des feuilles détachées de ces derniers afin de déterminer l'uniformité de l'infection croisée et d'examiner en détail les processus d'infection. Les isolats de CT obtenus de la matricaire inodore ont provoqué des symptômes de la maladie chez la matricaire inodore, mais pas chez la lentille ni chez le petit pois, même 14 jours après l'inoculation. Les isolats de CT issus de la lentille ont ...