Effect of Garlic Extract on Seed Germination, Seedling Health, and Vigour of Pathogen-Infested Wheat

The effect of garlic extract containing bioactive allicin on the germination and subsequent seedling vigour of pathogeninfested wheat seeds, was tested. The first aim was to characterize the antifungal activities of garlic extract and pure allicin, on the most frequently occurring wheat pathogens of the Helminthosporium genus (sensu lato) in Argentina. The second aim was to characterize the antifungal activities of garlic extract and pure allicin on moulds belonging to the natural endogenous microflora. Garlic extract showed fungicidal activity on the endogenous fungal contamination of the wheat seeds and particularly reduced the degree of disease caused by Bipolaris sorokiniana and Drechslera tritici-repentis. Allicin in garlic juice corrected the poor germination of wheat seeds caused by natural mycoflora of grain. Growth promoting activities of garlic juice on wheat seedling vigour was reported. Interestingly, the inoculum on naturally infected wheat seeds could be reduced with garlic juice as a seed dressing biofungicide, before sowing. In this study, we demonstrated the efficacy and the high control potential of garlic extract against seed-borne wheat fungi. Such results suggest that using garlic extract can minimise the risk of infection as well as minimise the risk of chemical fungicide exposure. On the basis of these results, scale-up to field trials using garlic extract and allicin as the dressing biofungicide before sowing for disinfection of wheat seeds, seems justified as a sustainable alternative to the use of chemical fungicides

Monitoring the Switch from Housekeeping to Pathogen Defense Metabolism in Arabidopsis thaliana Using cDNA Arrays

Plants respond to pathogen attack by deploying several defense reactions. Some rely on the activation of preformed components, whereas others depend on changes in transcriptional activity. Using cDNA arrays comprising 13,000 unique expressed sequence tags, changes in the transcriptome of Arabidopsis thaliana were monitored after attempted infection with the bacterial plant pathogen Pseudomonas syringae pv. tomato carrying the avirulence gene avrRpt2. Sampling at four time points during the first 24 h after infiltration revealed significant changes in the steady state transcript levels of ~650 genes within 10 min and a massive shift in gene expression patterns by 7 h involving ~2,000 genes representing many cellular processes. This shift from housekeeping to defense metabolism results from changes in regulatory and signaling circuits and from an increased demand for energy and biosynthetic capacity in plants fighting off a pathogenic attack. Concentrating our detailed analysis on the genes encoding enzymes in glycolysis, the Krebs cycle, the pentose phosphate pathway, the biosynthesis of aromatic amino acids, phenylpropanoids, and ethylene, we observed interesting differential regulation patterns. Furthermore, our data showed potentially important changes in areas of metabolism, such as the glyoxylate metabolism, hitherto not suspected to be components of plant defense

Relationship between transmembrane ion movements, production of reactive oxygen species and the hypersensitive response during the challenge of tobacco suspension cells by zoospores of Phytophthora nicotianae

Copyright © 2001 Academic Press. All rights reserved.We have examined the responses of suspension cultured tobacco cells after inoculation with zoospores from compatible or incompatible faces of the Oomycete pathogen Phytophthora nicotianae. The incompatible interaction, characterized by the production of reactive oxygen species (ROS) (specifically superoxide (HO2/O2-) and hydrogen peroxide (H2O2)), and by a hypersensitive response (HR), was not dependent upon the presence of exogenous calcium. However, perturbation of calcium ion movements by EGTA or LaCl3 suppressed both ROS production and the extent of cell death. The Ca2+-specific ionophore, A23187, slightly enhanced ROS production during the incompatible interaction but had no effect on the responses of susceptible or unchallenged cells. These results confirm that both ROS production and the HR are potentiated by movement of endogenous calcium across the plasmalemma. While there was no evidence of a transmembrane K+/H+ exchange immediately following incompatible zoospore challenge, a later potassium efflux from cells coincided with the onset of the HR. Unexpectedly, medium pH drifted downwards during all host cell responses suggesting that alkaline peroxidases are not the major source of ROS generation during an incompatible tobacco cell/zoospore interaction. © 2001 Academic Press.A. J. Able, D. I. Guest and M. W. Sutherlandhttp://www.elsevier.com/wps/find/journaldescription.cws_home/622932/description#descriptio