Tweddell, R. J. | Search bioRxiv

bioRxiv2025

GRAS salts and eastern hemlock extract: a dual approach to sustainable plant disease management‎‎

Several studies assessed the potential of salts and plant extracts as sustainable, eco-friendly phytosanitary products in plant protection. Here, we examined the efficacy of Generally Recognized as Safe (GRAS) salts sodium benzoate (SBE) and sodium bicarbonate (SBI) used alone or in combination with a twig extract from eastern hemlock (EH) against the bacterial pathogen Pseudomonas syringae pv. tomato DC3000 (Pst DC3000). The antimicrobial activity of the three products, and their ability to bolster host plant natural defenses, were assessed using the Arabidopsis-Pst DC3000 pathosystem as a model. RT-qPCR and leaf staining assays on a transgenic Arabidopsis line engineered to express reporter protein {beta}-glucuronidase under the control of pathogen-inducible promoter PR1 showed both GRAS salts and the EH extract to trigger the expression of salicylic acid (SA)-inducible genes. Salt- and EH extract-treated plants exhibited callose deposits in leaf tissue, further pointing to the induction of the SA signaling pathway and suggesting the establishment of a physical barrier in the leaf apoplast upon treatment. Direct toxicity measurements and a bacterial infection assay in growth chamber showed both GRAS salts and the EH extract to inhibit Pst DC3000 growth and Arabidopsis leaf colonization. Toxicity assays also revealed complementary, additive effects between the two salts and the EH extract in their detrimental effect against the pathogen, as evidenced by reduced minimum inhibitory concentrations when used in combination. Interestingly, SBE and SBI strongly delayed leaf senescence following infection, either alone or combined with the EH extract. Together, these findings confirm the potential of SBE, SBI and the EH twig extract as both toxic compounds against Pst DC3000 and natural defense stimulators in Arabidopsis. They also highlight the potential of GRAS salt and plant extract combinations as a sustainable alternative to chemical pesticides in plant pathogen management.

plant biology↗

bioRxiv2023

Forest tree extracts induce resistance to Pseudomonas syringae pv. tomato in Arabidopsis

BackgroundThe widespread use of conventional pesticides to control plant fungal and bacterial pathogens poses significant risks to human health and the environment, and there is an urgent need for safer and more sustainable alternatives in agricultural management. Studies have shown that plant extracts can be effective in controlling plant diseases either by directly targeting the pathogens or by reinforcing the host plants own defenses. Here, we examined the potential of ethanolic extracts from forest tree species eastern hemlock, English oak, eastern red cedar and red pine for their antibacterial activity against Pseudomonas syringae pv. tomato (Pst) strain DC3000 and the ability of these forestry by-products to trigger effective defense responses in the model plant Arabidopsis thaliana. ResultsThe four tree extracts exhibited direct toxic effects against Pst DC3000, as notably observed for the English oak extract inhibiting bacterial growth and showing bactericidal activity at relatively low concentrations. Using an Arabidopsis line expressing reporter protein {beta}-glucuronidase under the control of a salicylic acid-inducible pathogenesis-related protein gene promoter, the extracts were shown also to induce defense-related genes expression in leaf tissue. RT-qPCR assays with DNA primers for different gene markers further confirmed this conclusion and highlighted gene-inducing effects for the tree extracts triggering, at different rates, the expression of salicylic acid- and oxidative stress-responsive genes. The extracts direct antibacterial effects, combined with their defense gene-inducing effects in planta, resulted in a strong host plant-protecting effect against Pst DC3000 associated with bacterial growth rates reduced by [~]75 to 98% seven days post-infection, depending on the extract. ConclusionsThese findings show the effectiveness of tree extracts as eventual plant protectants against the plant bacterial pathogen Pst. In a broader perspective, they suggest the potential of these forestry by-products as a source of bioactive compounds useful in plant protection and as a sustainable, eco-friendly alternative to conventional synthetic pesticides for the management of economically important plant pathogens.

plant biology↗