The aim of the present study was to investigate the mechanisms of induced resistance after the application of specific elicitors (plant activators) in Vitis vinifera/Plasmopara viticola pathosystem. For this purpose phosphonate-containing elicitors, whose solo substances and a fungicide from the strobilurin group were applied on leaves of potted vines (Riesling, Müller-Thurgau, Solaris, Regent). The elicitors were used protectively and curatively. The characterization of the effect of the elicitors in planta, and detection was carried out by microscopic molecular level (qPCR, microarray).According to the assessment of the biological activity of the elicitors on leaves of potted vines, Frutogard®, algin Biovital®, phosphonate and phosphate showed the best results. The efficiencies were between 70% and 90%. The protective treatment was consistently more effective than curative. Autofluorescence measurements showed that tolerant varieties (cv. Regent; cv. Solaris) constitutively contain phenols. Induced and subsequently inoculated potted vines showed stronger autofluorescence than only inoculated plants. Transcriptome studies showed that phosphate and phosphonate led to similar defense responses through activation of stress-related signaling pathways. In this context, PR proteins, secondary metabolites e.g. Phytoalexins and enhanced cell wall metabolism were induced. Generally, systemic acquired resistance by salicylic acid pathway and PR proteins and induced systemic resistance through jasmonic acid and ethylene pathways have been activated. Elicitation with Frutogard® (without subsequent inoculation) induced stress-related pathways; however, less than phosphate and phosphonate did. These included stress signaling pathways, secondary metabolites, and hormones such as gibberellins and cytokinins. In the case of protective treatment with Frutogard® it induced even less stress-related signaling pathways.Based on the results obtained, specific instructions for the viticultural practices could be derived from this work, where the replacement of copper-containing pesticides for organic viticulture is in focus in this study.
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