<p>Drug-delivery nano-systems enhances the potency of bioactive molecules due to its increase membrane permeability, as a result of their sub-cellular size. The concept of engineered nano-carriers may be a promising route to address confounding challenges in agriculture that could lead to an increase in crop production while reducing the environmental impact associated with crop protection and food production. A key motivation of this work is to evaluate the potential use of drug delivery nanosystems in agriculture, especially in the area of disease control. To this end, identifying the most suitable materials to serve as carrier and cargo is imperative. Understanding their bioactive properties and their physical-chemical characteristics is critical because these influences not only their biological effects on plants and environmental impact, but also, the fabrication process and potential scaling-up, enabling practical and relevant field applications in the future. </p> <p> </p> <p>In this work, chitosan was selected as nano-carrier material because of its biological and chemical properties. The chemical structure of chitosan allows spontaneous assemble of core-shell like nanostructures via ionic gelation, has enabled it to be used as nano-carrier biomaterial intended for delivery of bioactive cargo. In agriculture, the use of chitosan is of special interest due to its immune-modulatory activity elicited in plants. However, due to its inherent molecular heterogenicity, the formulation and fabrication of stable and low inter-batch variability chitosan nanocarriers via ionic gelation is difficult and time consuming.</p> <p> </p> <p>A myriad of different bioactive molecules has been tested as payload, encapsulated into chitosan-based delivery nano-systems for a range of purposes ranging from biomedicine, pharmaceutical, food and agriculture. In this work plant derived essential oils were selected as bioactive payload. Essential oils are at the core of the plant communication process with their phytobiome, including plant pathogens. Molecules from essential oils can carry an air-borne message serving as a plant-to-plant communication system (a phenomenon known as allelopathy) that activate the plant defense mechanisms. Encapsulation of essential oils into chitosan nanocarriers is only possible by forming nano-emulsions. </p> <p>Despite the potential benefits from the use of chitosan and essential oils in agriculture, its use at a large scale has been hindered by the overwhelming inconsistencies in the current literature, regarding their formulation and fabrication. This work addresses these problems and presents evidence that support the feasibility of producing highly chitosan nanocarriers loaded with essential oils, in a facile and rapid way, using FDA-grade materials only, without the need of expensive or specialized instrumentation. </p> <p> </p> <p>The plant-pathogen compatible interaction between <i>A. thaliana</i> and <i>B. cinerea</i> was used as biological model to test the hypothesis that chitosan nano-carriers and essential oil nano-emulsions can enhance the quantitative disease resistance of plants against broad host-range necrotrophic pathogens. We found that these treatments display a dose-dependent response in plants triggering a systemic immune response. Image-based phenotyping analysis showed that chitosan nanoparticles alone, as well as loaded with d-limonene, significantly enhanced the disease resistance of <i>A. thaliana</i> against <i>B. cinerea</i>. Nano-emulsions using essential oils from cinnamon, clove, coriander and red thyme also produced similar effects on the defense response in the pathosystem under study. Functional analysis of the differentially expressed genes from treated plants revealed that these treatments up-regulated the biological process involved in “stress management”, while down-regulated the biological process required for normal growth and development during ideal, non-stressful conditions.</p>

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La brûlure foliaire causée par Alternaria dauci est la maladie foliaire la plus dommageable pour les cultures de carottes, entravant la récolte mécanique. Seuls des cultivars partiellement résistants sont connus et commercialisés, mais leurs niveaux de résistance sont insuffisants. Les mécanismes de la résistance quantitative des plantes aux agents pathogènes sont mal caractérisés. Nous avons choisi d'étudier ces mécanismes dans l'interaction A. dauci-carotte. Auparavant, plusieurs résultats expérimentaux convergents ont montré que la résistance aux toxines fongiques entre en jeu dans cette interaction. Les tests de toxicité effectués avec des suspensions cellulaires de carotte ont révélé une corrélation entre la résistance des carottes à A.dauci et la résistance des cellules de carotte aux exsudats du champignon. Ces résultats nous ont incités à étudier les toxines impliquées dans le pouvoir pathogène d'A. dauci et afin de pouvoir étudier la réponse de la plante à celles –ci. En utilisant les profils HPLC de la phase organique d'exsudats de différentes souches de champignons, nous avons découvert une corrélation entre la production de toxines et l’agressivité de ces souches suggérant que la production de toxines joue un rôle majeur dans l’interaction A. dauci-carotte. Nous avons effectué l'extraction, la purification et la caractérisation de l'une des molécules candidates que nous avons nommé aldaulactone. Nous avons démontré sa toxicité grâce à un nouveau protocole de quantification de cellules mortes et vivantes. Un transcriptome d’A. dauci et une étude de l’expression des gènes en fonction de la production d’aldaulactone ont été utilisées pour étudier sa voie de biosynthèse. / Alternaria leaf blight, caused by the necrotrophic fungus Alternaria dauci, is the most damaging foliar disease of carrots, especially because it hampers leaf-pull harvesting. Only partially – and insufficiently – resistant cultivars exist. In general, partial resistance mechanisms are poorly understood, so we chose to study them in this interaction. Previous results obtained in the lab highlighted a correlation between plant resistance to the fungus and plant cell resistance toward fungal toxins. It was also shown using carrot cell suspensions that fungal exudates’ toxicity was only present in the organic phase. These results led us to better characterize the toxins produced by A. dauci, in order to get a deeper understanding of carrot cell resistance mechanisms toward those toxins. HPLC analysis of the exudates from different fungal strain uncovered a correlation between toxin production and the aggressiveness of the fungal strains, suggesting that toxin production is an important component of said aggressiveness. We extracted, purified and characterize one of these candidates, and named it aldaulactone. Using a new image analysis protocol, we demonstrated the toxicity of Aldaulactone on carrot cell suspensions. Transcriptomic data from Alternaria dauci were used to explore the biosynthesis pathway of Aldaulactone. Candidate Genes were selected and their level of expression compared with aldaulactone production in various A. dauci cultures.

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