Phytochemical Constituents and Antimicrobial Activity of Euphorbia serrata L. Extracts for Borago officinalis L. Crop Protection

Abstract

The Euphorbia genus is the third-largest group of blooming plants, features a rich morphological variability, has a near-cosmopolitan distribution, and diverse medicinal uses. Nonetheless, phytochemical information about Euphorbia serrata L. extracts is not available. The objective of this research was to examine the constituents of the hydromethanolic extract of its aerial parts and propose valorization pathways. The results of gas chromatography-mass spectroscopy (GC−MS) demonstrated that 3-methylbutyl formate, quinic acid, N1-(4-hydroxybutyl)-N3-methylguanidine acetate, and 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one were the main phytocompounds, which have antimicrobial activity. Such activity was assayed against Pseudomonas cichorii, Botrytis cinerea, Fusarium oxysporum, and Sclerotinia sclerotiorum, four of the most destructive diseases of borage (Borago officinalis L.) crops, obtaining minimum inhibitory concentrations (MICs) of 750 and 1000 μg·mL−1 against the bacterium and the three fungal taxa, respectively, in in vitro tests. Conjugation of the extract with chitosan oligomers (COS) enhanced this activity, leading to MIC values of 187.5, 750, 500, and 500 μg·mL−1 for P. cichorii, B. cinerea, F. oxysporum, and S. sclerotiorum, respectively. Additional in vivo assays against two of the pathogens confirmed the protective action of the COS–E. serrata extract conjugate complexes on artificially inoculated plants at a dose of 375 and 1000 μg·mL−1 for P. cichorii and F. oxysporum, respectively. These findings suggest that this plant species can be a rich source of biorationals for prospective use in crop protection.