Antimicrobial Efficacy and HPLC Analysis of Polyphenolic Compounds in a Whole-Plant Extract of Eryngium campestre

Due to the constant increase in the number of plant diseases and the lack of available treatments, there has been a growing interest in plant extracts over the past few decades. Numerous studies suggest that plant extract molecules possess valuable antimicrobial activities, particularly against fungi and bacteria. This suggests that these biomaterials could potentially serve as attractive therapeutic options for the treatment of phytopathogen infections. In the present study, we investigated and analyzed the methanolic extract of Eryngium campestre L. whole plant extract using HPLC. The analysis revealed the presence of several polyphenolic constituents, with benzoic acid, catechol, quercetin, vanillic acid, resveratrol, naringenin, and quinol being the most abundant. The amounts of these constituents were determined to be 2135.53, 626.728, 579.048, 356.489, 323.41, 153.038, and 128.77 mg/kg, respectively. Furthermore, we isolated and identified different plant fungal and bacterial isolates from symptomatic potato plants, which were accessioned as Rhizoctonia solani (OQ880458), Fusarium oxysporum (OQ820156) and Fusarium solani (OQ891085), Ralstonia solanacearum (OQ878653), Dickeya solani (OQ878655), and Pectobacterium carotovorum (OQ878656). The antifungal activity of the extract was assessed using fungal growth inhibitions (FGI) at concentrations of 100, 200, and 300 µg/mL. The results showed that at the lowest concentration tested (100 µg/mL), the extract exhibited the highest effectiveness against R. solani with an FGI of 78.52%, while it was least effective against F. solani with an FGI of 61.85%. At the highest concentration tested, the extract demonstrated the highest effectiveness against R. solani and F. oxysporum, with FGIs of 88.89% and 77.04%, respectively. Additionally, the extract displayed a concentration-dependent inhibitory effect on all three bacterial pathogens. At the highest concentration tested (3000 µg/mL), the extract was able to inhibit the growth of all three bacterial pathogens, although the inhibition zone diameter varied. Among the bacterial pathogens, D. solani exhibited the highest sensitivity to the extract, as it showed the largest inhibition zone diameter at most of the extract concentrations. These findings highlight the potential of the E. campestre extract as a source of natural antimicrobial agents for controlling various plant pathogens. Consequently, it offers a safer alternative to the currently employed protective methods for plant disease management.