Lecture 8.pptx PDF

Use of natural substances Sara Francesconi, PhD [email protected] Types of substances There are many substances of natural origin useful for defense. Plants and microorgansims produce a vast heterogeneous range of primary and secondary metabolites that have proven useful for t...

Use of natural substances Sara Francesconi, PhD [email protected] Types of substances There are many substances of natural origin useful for defense. Plants and microorgansims produce a vast heterogeneous range of primary and secondary metabolites that have proven useful for the control of phytopathologies: - Fatty acids  polyketides - Phenilpropanoids  cinnamic acids, lignin, phenylpropenes, benzoic acids, coumarins - Aromatic polyketides flavonoids, stilbenes, flavolignans, isoflavonoids, terpenoid quinones - Terpens  hemiterpenes, monoterpenes, iridoids, sesquiterpenes, diterpenes, sesterpenes, triterpenes, saponins, phytosterols, vitamins, glycosides - Alkaloids  derivatives of alkaloids (many chemical modifications) including caffeine - Peptides - Cyanogenic glycosides and glucosinolates - Carbohydrates  pectins and oligogalacturonides Some molecules of natural origin also derive from the animal world and algae and have demonstrated capabilities broad-spectrum antimicrobial. Direct and indirect mechanisms of action often coexist. Direct mechanisms of action + ability to inhibit biofilm production Indirect mechanisms of action Types of substances – the most interesting ones with antimicrobial properties Phenols and phenolic acids  inhibit enzymes by interacting with sulfhydryl groups Quinones  Bind to adhesins (biofilms), cell wall polypeptides and membrane enzymes Flavones and flavonoids  Form a complex with the cell wall and destroy membrane permeability Tannins  Inactivate adhesins, enzymes, the cell capsule (biofilm), transport proteins, polysaccharides Coumarins  Inhibit microorganisms in vitro Terpenoids  They are lipophilic compounds that act on membrane permeability Alkaloids  intercalate DNA Lectins and polypeptides  They form channels in the membrane and compete with the molecules responsible for adhesion (biofilm) What are the main source for extraction? Concept of circular economy Circular economy and agriculture What are the main source for extraction? Some examples Some examples Frequent interest from agropharmaceutical companies in developing new agropharmaceuticals based on natural substances + increase in investments and interest in approval. Edible oils Obtained from seeds, flowers, leaves, trunks and mostly made up of triglycerides. Widely used in the food sector and also used as adjuvants in agrochemicals. Currently no edible oil is approved as a fungicide or bactericide in Italy. Italian legislation allows the use of sunflower oil, grape seed oil, olive oil, corn oil, soybean oil, peanut oil, corn oil, mustard oil, cotton oil as corroborators or enhancers of plant resistance. Essential oils Secondary metabolites contained in various parts of the plant of many plant species. They are aromatic metabolites and have a high volatility (unlike edible oils). They are made up of a wide range of heterogeneous metabolites, the main families are  terpenes, phenols, alcohols, ethers, aldehydes, ketones. Among the most frequent compounds we find  thymol, carvacrol, eugenol, menthol, limonene. Formulations based on sweet orange essential oil and cloves authorized in Italy as fungicides: - Sweet orange essential oil  consists of limonene. It has a dehydrating and dissolving action on membrane structures. It has a strong eradicating effect although short-lived. Liquid formula against powdery mildew, downy mildew, rust on vines, peach, citrus, horticultural and ornamental trees. - Clove essential oil  mixture of numerous molecules, eugenol prevails. In Italy it is approved as a liquid formulation alone or in a mixture with agrochemicals of synthetic origin for post-harvest treatments on fruit. Pure eugenol is also formulated with thymol and geraniol authorized for vegetation treatments against gray mold on vines. In this formulation, the active ingredients are encapsulated in microcapsules which regulate their release. Derived from algae Used as biostimulants of vegetative activity but also act as elicitors  laminarin  polysaccharide with a structure similar to the cell wall of pathogens  induces the production of SA and SAR. It is approved against scab and fire blight in pome fruits, powdery mildew in vines, powdery mildew and gray mold in strawberries. Polysaccharide extracts - Cerevisane  made up of cell walls of Saccharomyces cerevisiae  chitins, polysaccharides, mannose polymers and glucose. The formulation is a wettable powder approved against powdery mildew, downy mildew, botrytis on vines and various horticultural crops - COS-OGA  COS stands for chito-oligosaccharides and OGA stands for oligogalacturonides. Authorized against powdery mildew on vines, nightshades and cucurbits and downy mildew on salads. - Chitosan  It derives from the deacetylation of chitin, present in crustacean shells and fungal walls. High biocompatibility, biodegradability, bioactivity, low toxicity. It is approved as a basic substance by the European Union  admitted in organic farming and in integrated pest control protocols. Wide spectrum of action. Three mechanisms of action  direct, indirect, film-forming. Chitosan is positively charged, interacting with negatively charged molecules on membranes and nucleic acids. Effective in case of latent infections. The first formulations had to be dissolved at an acidic pH  not feasible for farmers, today there are wettable powders that dissolve in water at a neutral pH or concentrated solutions in the form of a gel. Optimal doses of use  0.5-1%. Basalt Flours® Local reality, corroborants allowed in organic, are moving for the defense in olive trees, vines, cereals. Tannins Other interesting molecules but not commercially available - Thiamine (vitamin B1) and riboflavin (vitamin B2)  induce SAR in tomato against Pst and in bean against gray mold - Quercetin  against gray mold - Azealaic acid, dehydrobetinal and pipecolic acid  are molecules produced during SAR, therefore they act in priming by increasing the synthesis of SA - Soya and casein protein hydrolysates  against P. viticola in vines - Volatile organic compounds (VOC)  messengers between plants but difficult to manage, interesting for post-harvest conservation - Pomegranate peel extracts Pros and Cons Pro Sustainability, no substances of synthetic origin are released into nature, possibility of exploiting waste from agricultural supply chains for extraction Cons Activity not always satisfactory, limited persistence, non-constant availability and characteristics (also linked to the extraction method) + difficulties in patent protection + possible problems of phytotoxicity and resistance selection linked to the application dose and time of use (especially for molecules that they only have direct antimicrobial action). Molecules 25, 4752; doi:10.3390/molecules25204752 Synthetic fungicides are not completely effective for the control of FHB; Fusarium strains resistant to fungicides are reported; Synthetic fungicides have several harmful effect on environment and human health; There is the need to find novel and eco-friendly compounds to control plant pathogens; We assayed the antifungal activity of Chitosan hydrochloride, its biostimulant effect on wheat, its ability to boost the SAR; Two durum wheat cultivars: Marco Aurelio (FHB-susceptible), DBC480 (FHB-resistant).  Fusarium head blight of wheat It is the most devasting wheat disease; Yield loss (10-70%) and grain quality reduction  mycotoxins! Causal agents: around 16 Fusarium spp. F. graminearum is the most aggressive and cosmopolitan. Khan et al., (2020) FHB in Italy: FHB occurs without a break since 1995; The prevalent species shifted from F. culmorum to F. graminearum and F. poae; FHB infection and mycotoxin accumulation increase from the South to the North; DON is the most frequent found and it is of particular concern for food safety. Scherm et al., (2013)  What Chitosan is Modified from Ifuku, (2014)  Results – in vitro antifungal experiments % of growth inhibition = 100 × (Mock-Treated/Mock) Results – biostimulant activity % of growth promotion = 100 × (Treated-Mock/Mock) Results – in vivo antifungal experiments Induction of SAR  Results – containment of FHB-associated compound accumulation The application of Chitosan The FHB-resistant behavior of hydrochloride reduced the DBC480 drastically reduced the amount of accumulated FHB- accumulated FHB-related related compounds in many compounds. cases.  Conclusions and perspectives – IV part Chitosan is a natural-derived, biodegradable product; It is a waste product that can be reused; Chitosan hydrochloride was able to control FHB in vitro and in vivo; It showed elicitor-like properties; The most promising strategy was to couple a resistant genotype and an eco- friendly antifungal molecule; Use of nanotechnologies to reduce the concentration of active molecules and to optimize their release.