Activity and mode of action of Parastrephia lepidophylla ethanolic extracts on phytopathogenic fungus strains of lemon fruit from Argentine Northwest

• Ethanolic extract is more active than aqueous extract.
• Parastrephia ethanolic extract inhibites conidia swelling and germination.
• The mycelium is less affected than the conidia.
• The ethanolic extract acts on the plasma membrane but not on the cell wall of myellium.
• The ethanolic extract decreases the incidence of green mold in fruit.

Fungal infections of fresh ripe Citrus limon fruit are the main cause of economic losses during their commercialization. The aim of this work was to evaluate the activity of the ethanolic extract (EE) from Parastrephia lepidophylla (Wedd.) Cabrera, a plant species that grows in the Argentine Northwest, on phytopatogenic fungi of lemon. Also, attempts were made to elucidate the mode of action of EE on the growth inhibition of phytopathogenic isolates of Penicillium digitatum Sacc. and Geotrichum citri-aurantii (Ferraris) E.E. Butler. The effect of the polyphenolic extracts on the conidia germination, mycelium growth and integrity of the plasma membrane was evaluated. The EE was active against both pathogens (minimal inhibitory concentration and minimal fungicidal concentration values of 150 μg of gallic acid equivalent/ml and 350 μg GAE/ml, respectively for both species). The conidia swelling and germination and the subsequent germ tube elongation was more affected by EE (100% inhibition at 200 μg GAE/ml) than the vegetative body of the fungus (50% inhibion at 400 μg GAE/ml). The fungus cell walls would not constitute a target for the EE components while the mechanism of action of the phytocomplex would be plasma membranes disruption. In vivo tests showed that P. leidophylla EE (700 μg GAE/ml) decreases the incidence of green mold disease in artificially inoculated lemons.