Extracts from native Argentinean plants for the control of Anthracnose

STEGMAYER, MI; ÁLVAREZ, NH; FAVARO, MA; REUTEMANN, AG; DERITA, MG

Conferencia; Plant productivity and food safety: Soil science, Microbiology, Agricultural Genetics and Food quality; 2022

The main cause of postharvest deterioration in agricultural products is fungaldiseases, among which anthracnose, caused by Colletotrichum spp., constitutes acosmopolitan disease for many tropical and subtropical fruits. The reductions in infectionsare made with fungicides whose toxicological risk, residues in food, and new legislation limit or prohibit their use. Plants protect themselves from fungal diseases through mechanisms that include physical and chemical barriers. In this work, the extraction and qualitative characterization of secondary metabolites from 12 species of Argentine native flora were carried out in search of this pathogen control.Hexane and methanolic extracts were obtained from dry ground material. Diffusiontests were carried out using 9 cm diameter sterile Petri dishes provided with four divisions so that each experiment was considered in quadruplicate. Extract solutions were prepared at a concentration of 50 mg mL -1 in DMSO and once dissolved, 400 µL of this stock solution were diluted in 20 mL of molten PDA culture medium. After vigorously shaking and before the mixture was solidified, 5 mL was poured into each of the four compartments of the Petridishes and cooled down. A conidia concentration between 10 4 and 10 5 CFU mL -1 wasinoculated inside a well located in the center of each compartment once the mediumcontaining 1000 ppm of each extract was solidified. Negative control was performed usingthe commercial antifungal Carbendazim® and a positive one (growth control), employing the solvent DMSO without plant extract. Once the mycelium of the control plates completely covered the surface of the medium (approximately 7 days), the measurements of the mycelium diameter that developed in each plate treated with each plant extract were carried out by scanning the plates for later reading and analysis with ImageJ® software. Thedifferences in the mean percentage of fungal growth in the presence of each extract werecompared with positive and negative controls by statistical analysis with a 95% confidenceinterval (CI). The hexane extract of Rapistrum rugosum flowers and Persicaria punctataleaves showed an inhibition consistent with the chemical control (p≤0.05).The hexane and methanolic extracts were analyzed using the thin layerchromatography (TLC) technique. Mixtures of hexane and ethyl acetate (proportions 8:2, 5:5, and 2:8) with defined polarity were used as eluting solvents. The TLC plates were observed under a UV light lamp at 254, 365 nm and visible light and exposed with p-anisaldehyde, Dragendorff, Ferric Chloride (FeCl 3 ), and Natural Products/Polyethylene glycol (NP/PEG).The chemical characterization revealed compounds such as, mono and sesquiterpenes,triterpene saponins, simple phenols, and polyphenols that would be involved in the inhibition.