Abstract
Plant diseases are a major cause for yield losses and new strategies to control them without harming the environment are urgently needed. Plant-associated bacteria contribute to their host’s health in diverse ways, among which the emission of disease-inhibiting volatile organic compounds (VOCs). We have previously reported that VOCs emitted by potato-associated bacteria caused strong in vitro growth inhibition of the late blight causing agent Phytophthora infestans. This work focuses on sulfur-containing VOCs (sVOCs) and demonstrates the high in planta protective potential of S-methyl methane thiosulfonate (MMTS), which fully prevented late blight disease in potato leaves and plantlets without phytotoxic effects, in contrast to other sVOCs. Short exposure times were sufficient to protect plants against infection. We further showed that MMTS’s protective activity was not mediated by the plant immune system but lied in its anti-oomycete activity. Using quantitative proteomics, we determined that different sVOCs caused specific proteome changes in P. infestans, indicating perturbations in sulfur metabolism, protein translation and redox balance. This work brings new perspectives for plant protection against the devastating Irish Famine pathogen, while opening new research avenues on the role of sVOCs in the interaction between plants and their microbiome.
Highlights
Plant diseases are a major cause for yield losses and new strategies to control them without harming the environment are urgently needed
Following an initial screen for P. infestans-inhibiting volatile organic compounds (VOCs) that revealed the high in vitro activity of sulfur-containing volatiles[19], we explored the capacity of three sulfurcontaining VOCs (sVOCs), DMDS, DMTS and methyl methane thiosulfonate (MMTS) to inhibit late blight in planta using leaf disc assays
Binocular observation confirmed that MMTS and DMTS totally prevented the development of P. infestans at the leaf surface (Fig. 1b)
Summary
Plant diseases are a major cause for yield losses and new strategies to control them without harming the environment are urgently needed. In our in vitro characterization of the biological effect of bacterial sVOCs on different life stages of P. infestans, the protective activity of DMDS was largely surpassed by that of two others sVOC, dimethyl trisulfide (DMTS) and S-methyl methane thiosulfonate (MMTS)[19] This latter compound, which is produced by Brassicaceae such as cabbage, cauliflower or broccoli, and by Liliaceae such as garlic[26], maintained high in vitro inhibition potential on all tested life stages of P. infestans even in very low concentrations[19], which raised the questions of its suitability as new plant protection product and of its mode(s) of action on plant and pathogen. The aims of the present study were i) to investigate the protective potential of MMTS and other selected sVOCs in planta using both potato leaf discs and plantlets, ii) to determine whether these sVOCs induced plant defences and/or acted directly on the pathogen, and iii) to define possible biological targets in P. infestans
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