Phytochemically characterized extracts from Polygonum species for the control of fruit phytopathogenic fungi

GISELA M. SEIMANDI; LAURA N. FERNANDEZ; MARÍA A. FAVARO; VERÓNICA E. RUIZ; MARCOS G. DERITA

Conferencia; Virtual International Conference - Plant productivity and food safety: Soil science, Microbiology, Agricultural Genetics and Food quality; 2021

Plant diseases caused by phytopathogenic fungi are responsible for economic losses arising mainly from crop yield reduction, but also resulting from diminished products quality and safety; sometimes they also represent a risk for human and animal health due to food contamination and the accumulation of toxic residues in the environment. Since regulations on the use of new and existing fungicides are becoming more and more stringent, it urges to identify and develop new chemical entities with fungicidal properties. Different naturally occurring compounds, semisynthetic derivatives, chitosan-based formulations and plant products including extracts or essential oils have been reported as part of this strategy. Polygonum acuminatum (Kunth) M.Gómez (Polygonaceae) is a perennial herb that grows in the central area of Argentina and it is commonly used by native populations to heal infected wounds and other ailments related to fungal infections. In this work, we explored the in vitro antifungal activity of its ethyl acetate extract, according to the CLSI guidelines, against a panel of five phytopathogenic fungi that greatly affect citrus, stone fruits and berries including: Penicillium digitatum, P. italicum, Monilinia fructicola, Botrytis cinerea and Rhizopus stolonifer. The sesquiterpenes isolated from the extract were also evaluated against these strains demonstrating that the dialdehyde polygodial was the responsible for this activity. In order to encourage the use of the extract rather than the pure compound, we displayed ex vivo assays using fresh oranges, peaches and strawberries inoculated with P. digitatum, M. fructicola and B. cinerea respectively, and subsequently treated by immersion with an extract solution of 250, 62.5 and 62.5 μg/mL concentration, respectively and according to the in vitro test results. For the ex vivo assay, 10 fruits each were superficially disinfected, inoculated with the appropriate pathogen, treated with the fungicides and incubated at the optimum conditions for each fungus. A set of 10 fruits each was used as positive control (treated with sterile water) and another set was used as negative control (treated with commercial fungicides). Then, the degree of sporulation (sporulation index) of P. digitatum (for oranges), M. fructicola (for peaches) and B. cinerea (for strawberries) on the surface of the decayed fruits was evaluated from a 0 to 4 scale, in which the value 0 was assigned to negligible sporulation and 4 referred to a dense fungal sporulation over the entire fruit. The index value for each fruit was treated as a biological replicate and the experimental data were analyzed statistically by a one-way ANOVA followed by Tukey?s multiple comparison test (α = 0.05) using the GraphPad Prism v.7.0 software. Results showed that both commercial fungicides and the plant extract significantly reduced the degree of fungal sporulation compared to the untreated control for the three fruit rots. The concentration of the active compound present in the extract used on fruit experiments was determined by GC-MS. Finally, cytotoxicity evaluation against Huh7 cells showed that P. acuminata extract was less cytotoxic than the commercial fungicides at the assayed concentrations.